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Rational function graphs

Learning goals

  • Distinguishes holes from vertical asymptotes of a rational function.
  • Finds intercepts and symmetry of a rational graph.
  • Uses asymptotes and signs to sketch rational branches.
  • Determines a rational function's range from its rule and graph.
  • Matches rational formulas to graphs using several features.
  • Checks what a limited graph window can establish about a rational function.

Click problems to add them to your worksheet.

Rational function graphs 1
Read the x-intercept of the rational graph. Give the answer as an ordered pair.
Figure for problem 561807

Hints

- Find where the curve actually crosses the horizontal axis. - What is the y-coordinate of any x-intercept?

Solution

1. The curve crosses the x-axis where the output is \(0\). 2. The crossing occurs at \(x=2\), so the x-intercept is \((2,0)\).

Answer

\((2,0)\).
Rational function graphs 2
For each graph, give the x-value missing from its domain. In which panel do both branches rise near that missing input?
Figure for problem 561808

Hints

- Look for the vertical gap that separates the branches in each graph. - Use the horizontal scale to read each gap's x-coordinate. - Compare whether the two sides of each gap move in the same or opposite vertical directions.

Solution

1. In panel a), the curve splits at \(x=2\), so that input is excluded. One branch falls while the other rises near it. 2. In panel b), both branches rise near \(x=-1\), so \(-1\) is excluded and panel b) has the same upward behavior on both sides.

Answer

a) Missing input: \(x=2\). b) Missing input: \(x=-1\); both branches rise in panel b).
Rational function graphs 3
Give the coordinates of the hole in the rational graph. Is the function defined at that x-value?
Figure for problem 561809

Hints

- Find the open circle rather than a filled point. - Read its horizontal and vertical coordinates separately. - Decide whether the missing point belongs to the graph.

Solution

1. The open circle lies at \((1,2)\). 2. An open circle indicates a missing point, so the function is not defined at \(x=1\), even though the nearby curve approaches height \(2\).

Answer

Hole: \((1,2)\). The function is not defined at \(x=1\).
Rational function graphs 4
The graph has no other zeros or excluded inputs. On which x-intervals is the function positive, and on which is it negative?
Figure for problem 561810

Hints

- Find the x-value where the branches are separated. - Compare each branch with the horizontal axis. - Write one open interval for each branch.

Solution

1. To the left of \(x=1\), the branch is above the x-axis, so outputs are positive for \(x<1\). 2. To the right of \(x=1\), the branch is below the x-axis, so outputs are negative for \(x>1\). 3. The input \(x=1\) is excluded.

Answer

Positive on \((-\infty,1)\); negative on \((1,\infty)\).
Rational function graphs 5
The function has no other zeros or excluded inputs beyond the graph. For which real x-values is it above the x-axis? Give intervals.
Figure for problem 561811

Hints

- Find every part of the curve above the horizontal axis. - Notice both its x-intercept and the place where the curve is undefined. - Give a separate interval for each positive region.

Solution

1. The curve crosses the x-axis at \(x=-2\) and has a vertical asymptote at \(x=1\). 2. The graph is above the x-axis to the left of \(-2\) and to the right of \(1\). 3. Neither boundary is included because the question asks where the output is strictly positive.

Answer

\((-\infty,-2)\) and \((1,\infty)\).
Rational function graphs 6
The dashed horizontal line is an asymptote of the curve. Does the curve ever reach the same height? If so, give one point where it does.
Figure for problem 561812

Hints

- Read the height of the dashed line from the vertical scale. - Look for any intersection between the curve and that line. - What does an intersection with the dashed line tell you about the height the function reaches?

Solution

1. The dashed line is \(y=2\). 2. The curve crosses that line at the point \((0,2)\), so the asymptote's height is attained.

Answer

Yes, at \((0,2)\).
Rational function graphs 7
At which vertical asymptote does the graph switch from negative outputs on the left to positive outputs on the right?
Figure for problem 561813

Hints

- Locate each place where the curve heads sharply up or down along a vertical line. - On each side of that line, is the curve above or below the x-axis? - Compare the two sides of both asymptotes before choosing.

Solution

1. At \(x=-2\), the nearby branches lie below the x-axis on both sides, so the sign does not switch. 2. At \(x=1\), the branch just to the left lies below the x-axis and the branch to the right lies above it. 3. The sign switches at \(x=1\).

Answer

\(x=1\).
Rational function graphs 8
Find the x-intercept of \(f(x)=\frac{2x-6}{x+2}\). Give its coordinates and check that the input is allowed.

Hints

- An x-intercept occurs where the function's output is zero. - When can a fraction equal zero? - Check the original denominator at any candidate input.

Solution

1. Set the numerator equal to zero: \(2x-6=0\), so \(x=3\). 2. The denominator at that input is \(3+2=5\), which is nonzero. 3. The x-intercept is \((3,0)\).

Answer

\((3,0)\); the denominator equals \(5\), so the point is allowed.
Rational function graphs 9
A rational function has these values: <table><tr><th>\(x\)</th><th>\(1\)</th><th>\(3\)</th></tr><tr><td>\(f(x)\)</td><td>\(1\)</td><td>\(-1\)</td></tr></table> Which graph, a) or b), matches the table? Explain using both signs.
Figure for problem 561816

Hints

- Check the height of each graph at the first input in the table. - Do the same at the second input, on the other side of the vertical gap. - Both table entries must match the same graph.

Solution

1. In panel a), the left branch is below the x-axis at \(x=1\) and the right branch is above it at \(x=3\). This disagrees with the table. 2. In panel b), the left branch has output \(1\) at \(x=1\) and the right branch has output \(-1\) at \(x=3\). 3. Therefore, panel b) matches.

Answer

Panel b).
Rational function graphs 10
Which graph has vertical asymptote \(x=-1\) and horizontal asymptote \(y=2\)?
Figure for problem 561817

Hints

- First find the panel whose branch separation is at the stated x-value. - More than one panel may pass the first check. - Then compare the horizontal level the curves approach far away.

Solution

1. Panels a) and c) have vertical asymptote \(x=-1\), while panel b) has vertical asymptote \(x=1\). 2. Panel a) approaches \(y=2\) far from the vertical asymptote, whereas panel c) approaches \(y=-2\). 3. Panel a) has both required asymptotes.

Answer

Panel a).
Rational function graphs 11
Let \(f(x)=\frac{2x^2+18}{x^2-6x+9}\). a) State the domain of \(f\) and find \(f(0)\). b) Show algebraically that \(f\) has no x-intercepts.

Hints

- Find where the denominator is zero. - Substitute \(x=0\) directly to find the y-intercept value. - A rational function equals zero only when its numerator is zero. - Can a real number have a negative square?

Solution

1. Factor the denominator: \(x^2-6x+9=(x-3)^2\). Therefore, \(D_f=\mathbb{R}\setminus\{3\}\). 2. Evaluate the function at zero: \(f(0)=\frac{18}{9}=2\). 3. An x-intercept would require \(2x^2+18=0\), or \(x^2=-9\). 4. This equation has no real solution, so \(f\) has no x-intercepts.

Answer

a) \(D_f=\mathbb{R}\setminus\{3\}\), and \(f(0)=2\) b) The function has no x-intercepts because \(2x^2+18=0\) has no real solutions.
Rational function graphs 12
The red graph \(g\) is a scaled version of the blue graph \(f(x)=\frac{2}{x^2+1}\). Describe the transformation and write \(g(x)\) in terms of \(f(x)\).
Figure for problem 534094

Hints

- Compare corresponding y-values at the same x-values. - Check whether the x-coordinates of key features remain unchanged. - A vertical scaling multiplies the entire function output.

Solution

1. The maximum value of \(f\) is \(2\), while the maximum value of \(g\) is \(1\). 2. At every x-value, the output of \(g\) is half the output of \(f\). For example, \(f(1)=1\) and \(g(1)=0.5\). 3. Therefore, the graph is vertically compressed by a factor of \(\frac{1}{2}\), and \(g(x)=\frac{1}{2}f(x)\).

Answer

Vertical compression by a factor of \(\frac{1}{2}\); \(g(x)=\frac{1}{2}f(x)\)
Rational function graphs 13
A mug of tea cools in a kitchen, while a cup of hot cocoa cools in a cooler room. Their temperatures \(T\), in degrees Celsius, after \(t\) minutes are modeled by \(g(t)=\frac{20t+180}{t+2}\) and \(h(t)=\frac{10t+160}{t+2}\), for \(t\ge0\). a) Decide whether graph \(k\) or graph \(m\) represents each function. Use the starting temperature. b) Find the horizontal asymptote of each function and explain what it means for the liquid.
Figure for problem 534118

Hints

- Substitute \(t=0\) to find each liquid's starting temperature. - Can you write each function as a constant plus a fraction that gets smaller as time passes? - What would the model predict after a very long time?

Solution

1. At \(t=0\), \(g(0)=\frac{180}{2}=90\,\text{°C}\) and \(h(0)=\frac{160}{2}=80\,\text{°C}\). 2. Graph \(k\) begins at \(90\,\text{°C}\), so it represents \(g\). Graph \(m\) begins at \(80\,\text{°C}\), so it represents \(h\). 3. Rewrite \(g(t)=20+\frac{140}{t+2}\) and \(h(t)=10+\frac{140}{t+2}\). 4. As \(t\) becomes large, the fractions approach zero, so the horizontal asymptotes are \(T=20\,\text{°C}\) and \(T=10\,\text{°C}\). These represent the two room temperatures in the models.

Answer

a) Graph \(k\): \(g\); graph \(m\): \(h\). b) For \(g\): \(T=20\,\text{°C}\); for \(h\): \(T=10\,\text{°C}\). Each is the room temperature approached by that liquid.
Rational function graphs 14
Match graphs \(f\), \(g\), and \(h\) to the correct descriptions. Explain briefly. 1. Vertical asymptote at \(x=-2\); hole at \(x=-1\). 2. Hole at \(x=1\); vertical asymptote at \(x=2\). 3. Vertical asymptotes at \(x=-2\) and \(x=2\); hole at \(x=0\).
Figure for problem 534130

Hints

- Find the x-values where each graph gets very high or low. - What does an open circle mark? - Read the x-coordinates carefully to distinguish the three descriptions.

Solution

1. In panel a), graph \(f\) has a vertical asymptote at \(x=2\) and a hole at \((1,-1)\). Thus, it matches description 2. 2. In panel b), graph \(g\) has a vertical asymptote at \(x=-2\) and a hole at \((-1,-1)\). Thus, it matches description 1. 3. In panel c), graph \(h\) has vertical asymptotes at \(x=-2\) and \(x=2\) and a hole at \((0,0)\). Thus, it matches description 3.

Answer

\(f\) (panel a): 2; \(g\) (panel b): 1; \(h\) (panel c): 3.
Rational function graphs 15
Read three features from the rational graph: a) the excluded x-value, b) the horizontal asymptote, c) the y-intercept as an ordered pair.
Figure for problem 561818

Hints

- Read the x-value of the vertical gap between branches. - Look for the horizontal height the graph approaches far from that gap. - The y-intercept is where the curve meets the vertical axis.

Solution

1. The graph has a vertical gap at \(x=2\), so \(x=2\) is excluded. 2. Far to either side, the graph approaches height \(1\), so the horizontal asymptote is \(y=1\). 3. The curve crosses the y-axis at the origin, so the y-intercept is \((0,0)\).

Answer

a) \(x=2\). b) \(y=1\). c) \((0,0)\).
Rational function graphs 16
The function has no other zeros or excluded inputs outside the displayed window. a) Read from the graph where \(r(x)\) is positive and where it is negative. Give intervals. b) At which of the three sign-change x-values is the function undefined? How can you tell from the graph?
Figure for problem 561820

Hints

- Check where each part of the curve lies relative to the x-axis. - Find the x-values where the sign changes. - At which values does the curve cross the axis, and at which is there a break?

Solution

1. Reading from left to right, the graph is below the x-axis on \((-\infty,-2)\), above it on \((-2,1)\), below it on \((1,3)\), and above it on \((3,\infty)\). 2. The graph crosses the x-axis at \(x=-2\) and \(x=3\). At those inputs, the output is zero. 3. At \(x=1\), the curve splits into branches that move sharply up and down. That input is excluded because it is a vertical asymptote.

Answer

a) Positive: \((-2,1)\) and \((3,\infty)\). Negative: \((-\infty,-2)\) and \((1,3)\). b) \(x=1\) is excluded: the graph has a vertical asymptote there. The other two values are x-intercepts.
Rational function graphs 17
What range does the rational graph suggest? Write an interval and say whether its lower boundary is included. Can a finite graph alone prove that this is the exact range for all real inputs?
Figure for problem 561821

Hints

- Find the lowest horizontal level the graph approaches. - Check whether the plotted curve reaches that level and whether its outputs seem bounded above. - Can you be certain about every input using only a finite drawing?

Solution

1. The plotted branches lie above \(y=2\) and appear to get closer to it without touching it. 2. The branches rise sharply near \(x=1\), suggesting no upper bound. The suggested range is \((2,\infty)\), with \(2\) excluded. 3. A finite graph cannot prove what happens at every input. A function rule or further reasoning is needed to confirm that the suggested range is exact.

Answer

Suggested range: \((2,\infty)\); \(2\) is excluded. No, a finite graph alone cannot prove the full range.
Rational function graphs 18
A student says the displayed graph represents \(f(x)=\frac{1}{x+2}+1\). Find two features of the graph that show the claim is incorrect.
Figure for problem 561822

Hints

- Read the vertical gap in the displayed graph. - Predict the vertical gap from the proposed denominator. - Compare the distant horizontal level with the proposed vertical shift.

Solution

1. The displayed graph has vertical asymptote \(x=2\), but \(f\) would have vertical asymptote \(x=-2\). 2. The displayed graph approaches the horizontal line \(y=2\), but \(f\) would approach \(y=1\). 3. The student is incorrect because both asymptotes disagree.

Answer

The graph's vertical asymptote is \(x=2\), not \(x=-2\); its horizontal asymptote is \(y=2\), not \(y=1\).
Rational function graphs 19
Let \(f(x)=\frac{x^2-4x+3}{x^2-1}\). State the domain of \(f\) and find all x-intercepts.

Hints

- Which values make the denominator zero? - A rational function equals zero when its numerator is zero and its denominator is nonzero. - Check every numerator zero against the domain.

Solution

1. Factor the denominator: \(x^2-1=(x-1)(x+1)\). Therefore, the domain is \(D_f=\mathbb{R}\setminus\{-1, 1\}\). 2. Factor the numerator: \(x^2-4x+3=(x-1)(x-3)\). Its zeros are \(x=1\) and \(x=3\). 3. An x-intercept must be in the domain. Since \(x=1\) is excluded, it is not an x-intercept. The only x-intercept occurs at \(x=3\), giving the point \((3, 0)\).

Answer

The domain is \(D_f=\mathbb{R}\setminus\{-1, 1\}\). The only x-intercept is \((3, 0)\).
Rational function graphs 20
Find the x-intercepts of each function. Account for the domain of each function. a) \(f(x)=\frac{2x+6}{x-3}\) b) \(g(x)=\frac{x^2-16}{x+4}\) c) \(h(x)=\frac{x^2-3x-10}{2x+5}\)

Hints

- When is a fraction equal to zero? - Which values are excluded by each denominator? - What happens when the same value makes both the numerator and denominator zero? - Factor each quadratic numerator when helpful.

Solution

1. For part a, set the numerator equal to zero: \(2x+6=0\), so \(x=-3\). The denominator is nonzero there, so the x-intercept is \((-3, 0)\). 2. For part b, factor the numerator: \(x^2-16=(x-4)(x+4)\). Its zeros are \(x=4\) and \(x=-4\), but \(x=-4\) is excluded because it makes the denominator zero. Thus, the only x-intercept is \((4, 0)\). 3. For part c, factor the numerator: \(x^2-3x-10=(x-5)(x+2)\). The zeros are \(x=5\) and \(x=-2\). The denominator is nonzero at both values, so the x-intercepts are \((5, 0)\) and \((-2, 0)\).

Answer

a) \((-3, 0)\) b) \((4, 0)\) c) \((5, 0)\) and \((-2, 0)\)
Rational function graphs 21
Find all x-intercepts of each function. a) \(p(x)=\frac{5}{x+2}-1\) b) \(q(x)=\frac{(x-1)(3x+2)}{x^2-9}\) c) \(r(x)=\frac{3x^2-12x+12}{x^2-4}\)

Hints

- Rewrite each equation so that one side equals zero. - When is a product equal to zero? - Check every candidate against the function’s domain. - What does it mean when a numerator zero is excluded by the denominator?

Solution

1. For part a, solve \(\frac{5}{x+2}-1=0\). Then \(\frac{5}{x+2}=1\), so \(x=3\). The denominator is nonzero, giving the x-intercept \((3, 0)\). 2. For part b, the numerator is zero when \(x-1=0\) or \(3x+2=0\). This gives \(x=1\) and \(x=-\frac{2}{3}\). Neither value is excluded by the denominator, so both are x-intercepts. 3. For part c, factor the numerator and denominator: \(3x^2-12x+12=3(x-2)^2\) and \(x^2-4=(x-2)(x+2)\). The only numerator zero is \(x=2\), but this value is excluded from the domain. Therefore, \(r\) has no x-intercepts.

Answer

a) \((3, 0)\) b) \((1, 0)\) and \(\left(-\frac{2}{3}, 0\right)\) c) No x-intercepts
Rational function graphs 22
Let \(g(x)=\frac{2x-6}{x^2-5x+6}\). State the domain of \(g\) and determine whether the function has any x-intercepts. Justify your answer.

Hints

- First find the zeros of the denominator. - What happens when the same value makes both the numerator and denominator zero? - An x-intercept must be a point where the function is defined and has output zero.

Solution

1. Factor the denominator: \(x^2-5x+6=(x-2)(x-3)\). Therefore, \(D_g=\mathbb{R}\setminus\{2, 3\}\). 2. Set the numerator equal to zero: \(2x-6=0\), so the only candidate is \(x=3\). 3. Since \(x=3\) is excluded from the domain, it cannot be an x-intercept. 4. Therefore, \(g\) has no x-intercepts.

Answer

\(D_g=\mathbb{R}\setminus\{2, 3\}\). The function has no x-intercepts because the only zero of the numerator, \(x=3\), is not in the domain.
Rational function graphs 23
Let \(f(x)=\frac{x^2-1}{x^2-2x+1}\) and \(g(x)=\frac{x+1}{x-1}\). Determine whether each statement is true or false. Explain your reasoning. a) The functions \(f\) and \(g\) have the same domain. b) To find the x-intercepts of \(f\), it is sufficient to solve \(x^2-1=0\).

Hints

- A rational function is undefined where its denominator is zero. - Is a zero of the numerator automatically an x-intercept? - Compare the denominator zeros of the two functions. - Every x-intercept must lie in the domain.

Solution

1. For \(f\), the denominator is \((x-1)^2\), so \(x=1\) is excluded. For \(g\), the denominator is \(x-1\), so \(x=1\) is also excluded. Thus, both domains are \(\mathbb{R}\setminus\{1\}\). 2. Solving \(x^2-1=0\) gives the numerator zeros \(x=1\) and \(x=-1\). 3. The value \(x=1\) is not in the domain of \(f\), so it is not an x-intercept. Only \(x=-1\) gives an x-intercept. 4. Therefore, part a is true, while part b is false because numerator zeros must still be checked against the domain.

Answer

a) True. Both functions have domain \(\mathbb{R}\setminus\{1\}\). b) False. Solving the numerator equation gives \(x=1\) and \(x=-1\), but \(x=1\) is excluded from the domain. The only x-intercept is \((-1, 0)\).
Rational function graphs 24
Let \(h(x)=\frac{x^2-4x}{x^2-16}\). Determine whether each statement is true or false. Explain your reasoning. a) The domain is \(D_h=\mathbb{R}\setminus\{4\}\). b) The function has an x-intercept at \(x=0\). c) The function has exactly two x-intercepts.

Hints

- Factor the quadratic denominator to find every excluded value. - For an x-intercept, the numerator must be zero and the denominator must be nonzero. - Simplifying the expression does not restore values excluded from the original domain. - Check each numerator zero individually.

Solution

1. Factor the denominator: \(x^2-16=(x-4)(x+4)\). Therefore, \(D_h=\mathbb{R}\setminus\{-4, 4\}\), so statement a is false. 2. Factor the numerator: \(x^2-4x=x(x-4)\). Its zeros are \(x=0\) and \(x=4\). 3. The value \(x=0\) is in the domain, so \((0, 0)\) is an x-intercept. Statement b is true. 4. The value \(x=4\) is excluded from the domain, so it is not an x-intercept. The function has only one x-intercept, making statement c false.

Answer

a) False. \(D_h=\mathbb{R}\setminus\{-4, 4\}\). b) True. \((0, 0)\) is an x-intercept. c) False. The function has exactly one x-intercept because \(x=4\) is excluded from the domain.
Rational function graphs 25
Consider \(f(x)=\frac{4x^2-16}{0.5x^2+2}\). a) Show that \(f\) is defined for every real number and that its graph has no vertical asymptotes. b) Determine whether the graph has symmetry about either coordinate axis or the origin. c) Find all x- and y-intercepts. d) Find the horizontal asymptote by analyzing \(f(x)\) as \(x\to\pm\infty\).

Hints

- Find the minimum possible value of the denominator. - Compare \(f(-x)\) with \(f(x)\) and \(-f(x)\). - Use \(x=0\) for the y-intercept and set the numerator equal to \(0\) for x-intercepts. - Compare leading coefficients for the end behavior.

Solution

1. Since \(0.5x^2+2\ge 2\) for every real \(x\), the denominator is never \(0\). Thus, the domain is all real numbers and there are no vertical asymptotes. 2. Because \(f(-x)=f(x)\), the function is even and the graph is symmetric about the y-axis. 3. The y-intercept is \(f(0)=-8\), so it is \((0, -8)\). For x-intercepts, solve \(4x^2-16=0\), giving \(x=\pm 2\). The x-intercepts are \((-2, 0)\) and \((2, 0)\). 4. For large positive or negative \(x\), the highest-degree terms control the fraction. Their coefficient ratio is \(\frac{4}{0.5}=8\), so the graph approaches the horizontal asymptote \(y=8\) at both ends.

Answer

a) Domain: \(\mathbb{R}\); no vertical asymptotes b) Symmetric about the y-axis c) y-intercept: \((0, -8)\); x-intercepts: \((-2, 0)\) and \((2, 0)\) d) Horizontal asymptote: \(y=8\)
Rational function graphs 26
Consider \(f(x)=\frac{x^2+1}{0.25x^2-4}\). a) Find the domain. b) Determine the graph's symmetry. c) Explain algebraically why the graph has no x-intercepts. d) Describe the behavior at each vertical asymptote and as \(x\to\pm\infty\).

Hints

- Set the denominator equal to \(0\) to find excluded values. - Compare \(f(-x)\) and \(f(x)\). - An x-intercept requires the numerator to equal \(0\). - Use one-sided sign analysis near each excluded value and compare leading coefficients for the end behavior.

Solution

1. Solve \(0.25x^2-4=0\). This gives \(x=\pm 4\), so the domain is \(\mathbb{R}\setminus\{-4, 4\}\). 2. Since \(f(-x)=f(x)\), the function is even and its graph is symmetric about the y-axis. 3. An x-intercept would require \(x^2+1=0\), which has no real solution. Therefore, there are no x-intercepts. 4. The numerator and denominator have the same degree, so the graph approaches the horizontal asymptote \(y=\frac{1}{0.25}=4\) at both ends. 5. The numerator is always positive. Near \(x=-4\), the denominator is positive on the left and negative on the right, so the graph rises without bound on the left and falls without bound on the right. 6. Near \(x=4\), the denominator is negative on the left and positive on the right, so the graph falls without bound on the left and rises without bound on the right.

Answer

a) \(\mathbb{R}\setminus\{-4, 4\}\) b) Symmetric about the y-axis c) No x-intercepts because \(x^2+1>0\) for all real \(x\) d) At \(x=-4\): rises without bound from the left and falls without bound from the right. At \(x=4\): falls without bound from the left and rises without bound from the right. As \(x\to\pm\infty\), \(f(x)\) approaches \(4\), so \(y=4\) is the horizontal asymptote.
Rational function graphs 27
Consider \(k(x)=\frac{2x^2-18}{x^2+2}\). a) Find the domain and determine the graph's symmetry. b) Find all x- and y-intercepts. c) Describe the end behavior as \(x\to\infty\) and as \(x\to-\infty\). d) Find \(k(1)\) and \(k(4)\).

Hints

- Can the denominator ever equal \(0\)? - Compare \(k(-x)\) with \(k(x)\). - Set \(x=0\) for the y-intercept and set the numerator equal to \(0\) for x-intercepts. - Compare leading coefficients for the end behavior.

Solution

1. Since \(x^2+2>0\) for all real \(x\), the domain is \(\mathbb{R}\). Also, \(k(-x)=k(x)\), so the graph is symmetric about the y-axis. 2. The y-intercept is \(k(0)=-9\), so it is \((0, -9)\). For x-intercepts, solve \(2x^2-18=0\), giving \(x=\pm 3\). The x-intercepts are \((-3, 0)\) and \((3, 0)\). 3. The numerator and denominator have the same degree and leading-coefficient ratio \(\frac{2}{1}=2\), so \(k(x)\) approaches \(2\) as \(x\) becomes very large in either direction. The horizontal asymptote is \(y=2\). 4. \(k(1)=\frac{-16}{3}\), and \(k(4)=\frac{14}{18}=\frac{7}{9}\).

Answer

a) Domain: \(\mathbb{R}\); symmetric about the y-axis b) y-intercept: \((0, -9)\); x-intercepts: \((-3, 0)\) and \((3, 0)\) c) \(k(x)\to 2\) as \(x\to\pm\infty\); horizontal asymptote: \(y=2\) d) \(k(1)=-\frac{16}{3}\), \(k(4)=\frac{7}{9}\)
Rational function graphs 28
Consider \(g(x)=\frac{x^2+5}{x^2+4x+6}\). a) State the domain of \(g\). b) Give the coordinates of the y-intercept. c) Explain mathematically why the graph has no x-intercepts.

Hints

- How can you determine whether a quadratic is ever zero? - What is the \(x\)-coordinate of every point on the y-axis? - What must be true of the numerator for a rational function to equal zero? - Can you find a positive lower bound for the numerator?

Solution

1. Complete the square in the denominator: \(x^2+4x+6=(x+2)^2+2\), which is positive for every real \(x\). Thus, \(D_g=\mathbb{R}\). 2. Evaluate \(g(0)\): \(g(0)=\frac{5}{6}\). Therefore, the y-intercept is \(\left(0, \frac{5}{6}\right)\). 3. The numerator satisfies \(x^2+5\geq 5>0\) for every real \(x\). Since it is never zero, the graph has no x-intercepts.

Answer

a) \(D_g=\mathbb{R}\) b) \(\left(0, \frac{5}{6}\right)\) c) There are no x-intercepts because \(x^2+5\) is positive for every real \(x\).
Rational function graphs 29
Consider \(f(x)=\frac{x}{x^2-4}\), \(g(x)=\frac{4x}{x^2-4}\), and \(h(x)=\frac{x^2+1}{x^2-4}\). a) Find the common domain and the equations of the vertical asymptotes shared by all three functions. b) Find \(f(3)\), \(g(3)\), \(h(3)\), \(f(0)\), \(g(0)\), and \(h(0)\). c) Describe the transformation that maps the graph of \(f\) to the graph of \(g\). d) Find the x-intercepts of each function.

Hints

- Factor the common denominator. - A rational function is zero when its numerator is zero and its denominator is nonzero. - Compare \(g(x)\) directly with \(f(x)\) to identify the transformation.

Solution

1. The common denominator factors as \((x-2)(x+2)\). No numerator cancels either factor, so the domain is \(\mathbb{R}\setminus\{-2, 2\}\), and the vertical asymptotes are \(x=-2\) and \(x=2\). 2. \(f(3)=\frac{3}{5}=0.6\), \(g(3)=\frac{12}{5}=2.4\), and \(h(3)=2\). Also, \(f(0)=0\), \(g(0)=0\), and \(h(0)=-\frac{1}{4}\). 3. Since \(g(x)=4f(x)\), the graph of \(g\) is a vertical stretch of the graph of \(f\) by a factor of \(4\). 4. The functions \(f\) and \(g\) have the x-intercept \((0, 0)\). The numerator \(x^2+1\) has no real zeros, so \(h\) has no x-intercepts.

Answer

a) Domain: \(\mathbb{R}\setminus\{-2, 2\}\); vertical asymptotes: \(x=-2\) and \(x=2\) b) \(f(3)=0.6\), \(g(3)=2.4\), \(h(3)=2\); \(f(0)=0\), \(g(0)=0\), \(h(0)=-\frac{1}{4}\) c) Vertical stretch by a factor of \(4\) d) \(f\) and \(g\): \((0, 0)\); \(h\): no x-intercepts
Rational function graphs 30
Consider \(p(x)=\frac{2}{x^2-9}\), \(q(x)=\frac{-2}{x^2-9}\), and \(r(x)=\frac{2x^2}{x^2-9}\). a) Determine whether each graph is symmetric about the y-axis. b) Find the horizontal asymptote of each function by analyzing the end behavior as \(x\to\pm\infty\). c) Describe the relationship between the graphs of \(p\) and \(q\).

Hints

- What happens when \(x\) is replaced by \(-x\) in an even power? - Compare the degrees and leading coefficients for the end behavior. - Multiplying all function values by \(-1\) produces which reflection?

Solution

1. Each formula contains only even powers of \(x\), so \(p(-x)=p(x)\), \(q(-x)=q(x)\), and \(r(-x)=r(x)\). All three graphs are symmetric about the y-axis. 2. For \(p\) and \(q\), the denominator has greater degree than the numerator, so both functions approach \(0\). Their horizontal asymptote is \(y=0\). 3. For \(r\), the numerator and denominator have the same degree, and the ratio of leading coefficients is \(2\). Its horizontal asymptote is \(y=2\). 4. Since \(q(x)=-p(x)\), the graph of \(q\) is the reflection of the graph of \(p\) across the x-axis.

Answer

a) All three graphs are symmetric about the y-axis. b) \(p\) and \(q\): \(y=0\); \(r\): \(y=2\) c) The graph of \(q\) is the reflection of the graph of \(p\) across the x-axis.
Rational function graphs 31
Consider \(f(x)=\frac{12}{x^2+3}\). a) Determine the graph's symmetry. b) Find \(f(-3)\), \(f(0)\), and \(f(3)\). c) Describe the end behavior as \(x\to\pm\infty\) and give the equation of the horizontal asymptote. d) Explain without further calculation why \(f\) has no x-intercepts.

Hints

- Compare \(f(-x)\) with \(f(x)\). - Substitute the given x-values directly. - What happens when a constant numerator is divided by a denominator that grows without bound? - When can a rational expression equal \(0\)?

Solution

1. Since \(f(-x)=f(x)\), the function is even and its graph is symmetric about the y-axis. 2. \(f(-3)=1\), \(f(0)=4\), and \(f(3)=1\). 3. The denominator has greater degree than the numerator, so the function approaches \(0\) as \(x\) becomes very large positive or negative. The horizontal asymptote is \(y=0\). 4. A rational function can equal \(0\) only when its numerator is \(0\). The numerator is the nonzero constant \(12\), so there are no x-intercepts.

Answer

a) Symmetric about the y-axis b) \(f(-3)=1\), \(f(0)=4\), \(f(3)=1\) c) \(f(x)\to 0\) as \(x\to\pm\infty\); horizontal asymptote: \(y=0\) d) No x-intercepts
Rational function graphs 32
Consider \(g(x)=\frac{-10}{x^2+2}\). a) Show algebraically that the graph is symmetric about the y-axis. b) Find the y-intercept and \(g(2)\). c) Explain from the formula why the range of \(g\) is \([-5, 0)\). d) Describe the end behavior for large \(\lvert x\rvert\).

Hints

- Compare \(g(-x)\) with \(g(x)\). - Find the smallest possible denominator. - Use the signs of the numerator and denominator to determine whether the function can be positive or zero. - Consider what happens as the denominator becomes very large.

Solution

1. \(g(-x)=\frac{-10}{(-x)^2+2}=\frac{-10}{x^2+2}=g(x)\), so the graph is symmetric about the y-axis. 2. \(g(0)=-5\), so the y-intercept is \((0, -5)\). Also, \(g(2)=\frac{-10}{6}=-\frac{5}{3}\). 3. Since \(x^2+2\ge 2\), the denominator is positive and has its smallest value at \(x=0\). Thus, the minimum function value is \(-5\). All values are negative, and they approach but never equal \(0\). Therefore, the range is \([-5, 0)\). 4. As \(x\to\pm\infty\), the denominator grows without bound, so \(g(x)\to 0\).

Answer

a) \(g(-x)=g(x)\), so the graph is symmetric about the y-axis. b) y-intercept: \((0, -5)\); \(g(2)=-\frac{5}{3}\) c) Range: \([-5, 0)\) d) \(g(x)\to 0\) as \(x\to\pm\infty\)
Rational function graphs 33
Consider \(f(x)=\frac{x}{x^2-2.25}\). a) Determine the graph's symmetry and find \(f(0)\) and \(f(1)\). b) Find the domain and all vertical asymptotes. State whether the function changes sign across each vertical asymptote. c) Describe the end behavior as \(x\to\infty\) and as \(x\to-\infty\).

Hints

- Compare \(f(-x)\) with \(f(x)\) and \(-f(x)\). - Set the denominator equal to \(0\). - The multiplicity of a denominator zero helps determine whether the sign changes. - Compare the degrees for the end behavior.

Solution

1. Since \(f(-x)=-f(x)\), the function is odd and its graph is symmetric about the origin. 2. \(f(0)=0\), and \(f(1)=\frac{1}{1-2.25}=-0.8\). 3. Solve \(x^2-2.25=0\), giving \(x=\pm 1.5\). Thus, the domain is \(\mathbb{R}\setminus\{-1.5, 1.5\}\). 4. Each excluded value is a simple zero of the denominator and is not a zero of the numerator. Therefore, \(x=-1.5\) and \(x=1.5\) are vertical asymptotes, and the function changes sign across each one. 5. The denominator has greater degree than the numerator, so \(f(x)\to 0\) as \(x\to\pm\infty\).

Answer

a) Symmetric about the origin; \(f(0)=0\), \(f(1)=-0.8\) b) Domain: \(\mathbb{R}\setminus\{-1.5, 1.5\}\); vertical asymptotes: \(x=-1.5\) and \(x=1.5\), with a sign change at each c) \(f(x)\to 0\) as \(x\to\pm\infty\)
Rational function graphs 34
Consider \(g(x)=\frac{2x^2-2}{9-x^2}\). a) Show algebraically that the graph is symmetric about the y-axis. b) Find the domain and all vertical asymptotes. c) Find the horizontal asymptote. d) Find the x-intercepts.

Hints

- Replace \(x\) with \(-x\) to test symmetry. - Set the denominator equal to \(0\) to find excluded values. - Compare leading coefficients for the horizontal asymptote. - Set the numerator equal to \(0\) for x-intercepts.

Solution

1. Since \(g(-x)=g(x)\), the function is even and its graph is symmetric about the y-axis. 2. The denominator is zero when \(9-x^2=0\), so \(x=\pm 3\). The domain is \(\mathbb{R}\setminus\{-3, 3\}\), and the vertical asymptotes are \(x=-3\) and \(x=3\). 3. The numerator and denominator have the same degree. The ratio of leading coefficients is \(\frac{2}{-1}=-2\), so the horizontal asymptote is \(y=-2\). 4. Solve \(2x^2-2=0\), giving \(x=\pm 1\). Thus, the x-intercepts are \((-1, 0)\) and \((1, 0)\).

Answer

a) \(g(-x)=g(x)\), so the graph is symmetric about the y-axis. b) Domain: \(\mathbb{R}\setminus\{-3, 3\}\); vertical asymptotes: \(x=-3\) and \(x=3\) c) Horizontal asymptote: \(y=-2\) d) x-intercepts: \((-1, 0)\) and \((1, 0)\)
Rational function graphs 35
Consider \(f(x)=\frac{4}{x^2-25}+0.2\). a) Show that the graph is symmetric about the y-axis. b) Show that the x-intercepts occur at \(x=-\sqrt{5}\) and \(x=\sqrt{5}\), and verify that \((0, 0.04)\) lies on the graph. c) Describe the end behavior as \(x\to-\infty\) and \(x\to\infty\). Give the equation of the horizontal asymptote.

Hints

- Compare \(f(-x)\) with \(f(x)\). - Set the function equal to \(0\) to find x-intercepts. - Substitute \(x=0\) to check the given point. - What happens to the rational term as \(\lvert x\rvert\) becomes large?

Solution

1. Since \(f(-x)=f(x)\), the function is even and its graph is symmetric about the y-axis. 2. Solve \(\frac{4}{x^2-25}+0.2=0\). Then \(4=-0.2(x^2-25)\), so \(x^2=5\), giving \(x=\pm\sqrt{5}\). 3. Evaluate \(f(0)=\frac{4}{-25}+0.2=-0.16+0.2=0.04\), so \((0, 0.04)\) lies on the graph. 4. As \(x\) becomes very large positive or negative, \(\frac{4}{x^2-25}\) approaches \(0\). Thus \(f(x)\) approaches \(0.2\) at both ends, and the horizontal asymptote is \(y=0.2\).

Answer

a) Symmetric about the y-axis b) x-intercepts: \((-\sqrt{5}, 0)\) and \((\sqrt{5}, 0)\); \(f(0)=0.04\) c) \(f(x)\to 0.2\) as \(x\to\pm\infty\); horizontal asymptote: \(y=0.2\)
Rational function graphs 36
Consider \(f(x)=\frac{3x^2+9}{(2x-4)(2x+4)}\). a) Find the domain and all vertical asymptotes. b) Find the horizontal asymptote. c) Explain algebraically why the graph has no x-intercepts. d) Determine the graph's symmetry and find the y-intercept.

Hints

- Set each denominator factor equal to \(0\). - Compare the leading coefficients after expanding the denominator. - An x-intercept requires the numerator to equal \(0\). - Compare \(f(-x)\) with \(f(x)\), and use \(x=0\) for the y-intercept.

Solution

1. The denominator is zero at \(x=-2\) and \(x=2\). The numerator is nonzero at both values, so the domain is \(\mathbb{R}\setminus\{-2, 2\}\), and the vertical asymptotes are \(x=-2\) and \(x=2\). 2. Since \((2x-4)(2x+4)=4x^2-16\), the numerator and denominator have the same degree. The horizontal asymptote is \(y=\frac{3}{4}\). 3. An x-intercept would require \(3x^2+9=0\), or \(x^2=-3\), which has no real solution. 4. Because \(f(-x)=f(x)\), the graph is symmetric about the y-axis. Also, \(f(0)=\frac{9}{-16}=-\frac{9}{16}\), so the y-intercept is \(\left(0, -\frac{9}{16}\right)\).

Answer

a) Domain: \(\mathbb{R}\setminus\{-2, 2\}\); vertical asymptotes: \(x=-2\) and \(x=2\) b) Horizontal asymptote: \(y=\frac{3}{4}\) c) No x-intercepts d) Symmetric about the y-axis; y-intercept: \(\left(0, -\frac{9}{16}\right)\)
Rational function graphs 37
Consider \(g(x)=\frac{3x^2}{x^2-1}\), with domain \(\mathbb{R}\setminus\{-1,1\}\). a) Show that the graph does not intersect the line \(y=3\). b) Find the range of \(g\).

Hints

- Test the proposed output \(y=3\) by solving the corresponding equation. - Split the domain into intervals on which \(x^2-1\) has the same sign. - On each interval, identify which output values are possible and which boundary values are approached but not reached.

Solution

1. Set \(g(x)=3\): \(\frac{3x^2}{x^2-1}=3\). Multiplying by the nonzero denominator gives \(3x^2=3x^2-3\), a contradiction. Thus the graph never reaches \(y=3\). 2. For \(|x|>1\), rewrite \(g(x)=3+\frac{3}{x^2-1}\). The fraction is positive, so \(g(x)>3\). It approaches \(3\) for large \(|x|\) and grows without bound near \(x=\pm1\) from outside. This gives outputs \((3,\infty)\). 3. For \(-1<x<1\), the denominator is negative and the numerator is nonnegative. Thus \(g(x)\le0\), with \(g(0)=0\); the outputs decrease without bound near the excluded inputs from inside. This gives \((-\infty,0]\). 4. Combining these sets, the range is \((-\infty,0]\cup(3,\infty)\).

Answer

a) The equation leads to \(0=-3\), so there is no intersection. b) \((-\infty,0]\cup(3,\infty)\)
Rational function graphs 38
For each \(t>0\), define \(g_t(x)=\frac{2x^2+t}{x^2+2t}\). a) Explain why the domain is all real numbers and why the function has no x-intercepts. b) Show that every graph passes through \((0, 0.5)\). c) Describe the end behavior of \(g_t\) and explain why the result is the same for every value of \(t\).

Hints

- Use \(x^2\ge 0\) and \(t>0\) to determine the signs of the numerator and denominator. - Substitute \(x=0\). - Compare the leading coefficients or divide by \(x^2\).

Solution

1. Since \(t>0\), both \(x^2+2t\) and \(2x^2+t\) are positive for every real \(x\). Thus, the domain is \(\mathbb{R}\), and there are no x-intercepts. 2. Evaluate \(g_t(0)=\frac{t}{2t}=\frac{1}{2}=0.5\), so every graph passes through \((0, 0.5)\). 3. Divide the numerator and denominator by \(x^2\) for nonzero \(x\): \(g_t(x)=\frac{2+\frac{t}{x^2}}{1+\frac{2t}{x^2}}\). 4. As \(x\) becomes very large positive or negative, the terms containing \(\frac{1}{x^2}\) approach \(0\). Therefore, the function approaches \(2\) at both ends. This is independent of \(t\) because the leading coefficients are always \(2\) and \(1\).

Answer

a) Domain: \(\mathbb{R}\); no x-intercepts b) \(g_t(0)=0.5\) c) \(g_t(x)\to 2\) as \(x\to\pm\infty\); horizontal asymptote: \(y=2\), independent of \(t\)
Rational function graphs 39
Consider the family \(f_k(x)=\frac{kx^2-18}{(x-3)(x+2)}\), with domain \(\mathbb{R}\setminus\{-2, 3\}\). a) Find the horizontal asymptote in terms of \(k\). b) Show that \(f_k\) has no x-intercepts when \(k\le 0\). c) Find the value of \(k\) for which the graph has a hole at \(x=3\). Then find the coordinates of the hole.

Hints

- Compare leading coefficients for the horizontal asymptote. - Analyze when \(kx^2=18\) can have real solutions. - A hole occurs when the same factor appears in the numerator and denominator. - Evaluate the simplified expression at the excluded x-value to locate the hole.

Solution

1. The numerator and denominator have the same degree and leading-coefficient ratio \(k\), so the horizontal asymptote is \(y=k\). 2. X-intercepts require \(kx^2-18=0\). If \(k=0\), this becomes \(-18=0\). If \(k<0\), then \(x^2=\frac{18}{k}<0\). Thus, there are no real x-intercepts for \(k\le 0\). 3. For \(x=3\) to be a hole rather than a vertical asymptote, the numerator must also be zero there: \(9k-18=0\), so \(k=2\). 4. For \(k=2\), \(f_2(x)=\frac{2(x-3)(x+3)}{(x-3)(x+2)}=\frac{2(x+3)}{x+2}\) for \(x\neq 3,-2\). The graph approaches the height \(\frac{2(6)}{5}=\frac{12}{5}\) as \(x\) approaches \(3\). The hole is \(\left(3, \frac{12}{5}\right)\).

Answer

a) \(y=k\) b) No x-intercepts for \(k\le 0\) c) \(k=2\); hole: \(\left(3, \frac{12}{5}\right)\)
Rational function graphs 40
Consider the family \(g_a(x)=\frac{2x^2+a}{x^2-16}\), where \(a\in\mathbb{R}\). a) Show that every graph has the same horizontal asymptote, and give its equation. b) Assume the rational expression is fully reduced. Find all values of \(a\) for which \(g_a\) has exactly two x-intercepts. c) For \(a=0\), find all vertical asymptotes.

Hints

- Compare leading coefficients. - Determine when \(x^2=-\frac{a}{2}\) has two real solutions. - Check whether either denominator zero also makes the numerator zero. - For \(a=0\), test the numerator at \(x=\pm 4\).

Solution

1. The numerator and denominator have the same degree, and the ratio of leading coefficients is \(2\). Therefore, every graph has horizontal asymptote \(y=2\). 2. X-intercepts satisfy \(2x^2+a=0\), or \(x^2=-\frac{a}{2}\). There are exactly two real solutions when \(a<0\). 3. The denominator is zero at \(x=\pm 4\). To keep the expression fully reduced, the numerator cannot also be zero there. Since \(2(4^2)+a=32+a\), require \(a\neq-32\). Thus, \(a<0\) and \(a\neq-32\). 4. For \(a=0\), the numerator is nonzero at \(x=\pm 4\), so the vertical asymptotes are \(x=-4\) and \(x=4\).

Answer

a) \(y=2\) b) \(a<0\) and \(a\neq-32\) c) \(x=-4\) and \(x=4\)
Rational function graphs 41
Consider \(f(x)=\frac{1}{x-2}+2\) and \(g(x)=2-\frac{1}{x^2}\), each on its domain. Find the coordinates of all intersection points of their graphs.

Hints

- Set the two function expressions equal. - Subtract the common constant term first. - Clear the denominators while keeping track of excluded values. - Substitute each valid x-value into either function.

Solution

1. Set the functions equal: \(\frac{1}{x-2}+2=2-\frac{1}{x^2}\), with \(x\neq 0, 2\). 2. Subtract \(2\): \(\frac{1}{x-2}=-\frac{1}{x^2}\). 3. Clear the denominators to get \(x^2=-(x-2)\), so \(x^2+x-2=0\). 4. Factor: \((x+2)(x-1)=0\), giving \(x=-2\) and \(x=1\). Both are in the common domain. 5. Evaluate \(f(1)=1\) and \(f(-2)=\frac{7}{4}\).

Answer

The intersection points are \((1, 1)\) and \(\left(-2, \frac{7}{4}\right)\).
Rational function graphs 42
Consider \(f(x)=\frac{4}{x-3}\) and \(g(x)=\frac{-4}{(x-1)^2}\). a) Find all vertical and horizontal asymptotes of both graphs. b) Find all intersection points of the graphs.

Hints

- Find denominator zeros and compare degrees. - Set the two function expressions equal. - Clear denominators and solve the resulting quadratic equation. - Verify that each solution lies in both domains.

Solution

1. For \(f\), the vertical asymptote is \(x=3\), and the horizontal asymptote is \(y=0\). 2. For \(g\), the vertical asymptote is \(x=1\), and the horizontal asymptote is \(y=0\). 3. Set the functions equal: \(\frac{4}{x-3}=\frac{-4}{(x-1)^2}\), where \(x\neq 1, 3\). 4. Clear the denominators to get \((x-1)^2=-(x-3)\). This simplifies to \(x^2-x-2=0\), so \(x=2\) or \(x=-1\). 5. Evaluate \(f(2)=-4\) and \(f(-1)=-1\).

Answer

a) \(f\): vertical \(x=3\), horizontal \(y=0\); \(g\): vertical \(x=1\), horizontal \(y=0\) b) \((2, -4)\) and \((-1, -1)\)
Rational function graphs 43
Determine the number of intersection points of the graphs in each pair. a) \(f(x)=\frac{x^2-2x+3}{x-2}\) and \(g(x)=2x-1\) b) \(f(x)=\frac{2}{x-1}+1\) and \(g(x)=\frac{x+3}{x+1}\)

Hints

- Set the function expressions equal. - Clear denominators while keeping track of excluded values. - Use the discriminant to determine the number of real solutions to a quadratic equation. - A contradiction means the graphs do not intersect.

Solution

1. For a), set the functions equal and clear the denominator: \(x^2-2x+3=(2x-1)(x-2)\). This simplifies to \(x^2-3x-1=0\). 2. The discriminant is \(13>0\), so the equation has two distinct real solutions. Neither solution is the excluded value \(x=2\). Therefore, there are two intersection points. 3. For b), rewrite the left side as \(\frac{x+1}{x-1}\), then set \(\frac{x+1}{x-1}=\frac{x+3}{x+1}\). 4. Cross-multiplication gives \((x+1)^2=(x+3)(x-1)\), which simplifies to the contradiction \(1=-3\). Therefore, there are no intersection points.

Answer

a) \(2\) intersection points b) \(0\) intersection points
Rational function graphs 44
Find all intersection points of \(f(x)=\frac{x^2-4x+3}{x-2}\) and \(g(x)=3x-9\).

Hints

- Set the two functions equal. - Clear the denominator and solve the resulting quadratic equation. - Check each solution against the domain. - Substitute valid x-values into the line to find the y-coordinates.

Solution

1. Set the functions equal, with \(x\neq 2\): \(\frac{x^2-4x+3}{x-2}=3x-9\). 2. Clear the denominator: \(x^2-4x+3=(3x-9)(x-2)\). 3. Simplify to \(2x^2-11x+15=0\), which factors as \((2x-5)(x-3)=0\). 4. Thus, \(x=\frac{5}{2}\) or \(x=3\). Both values are in the domain. 5. Evaluate \(g\left(\frac{5}{2}\right)=-\frac{3}{2}\) and \(g(3)=0\).

Answer

The intersection points are \(\left(\frac{5}{2}, -\frac{3}{2}\right)\) and \((3, 0)\).
Rational function graphs 45
Find all intersection points of \(f(x)=\frac{2}{x^2-1}\) and \(g(x)=\frac{1}{x-1}-1\).

Hints

- Identify all excluded x-values first. - Multiply by the least common denominator. - Check every algebraic solution against the original domains. - Substitute the valid x-value into either function.

Solution

1. The common domain excludes \(x=-1\) and \(x=1\). 2. Set the functions equal: \(\frac{2}{x^2-1}=\frac{1}{x-1}-1\). 3. Multiply by \((x-1)(x+1)\): \(2=x+1-(x^2-1)\). 4. Simplify to \(x^2-x=0\), so \(x=0\) or \(x=1\). 5. The value \(x=1\) is excluded. For \(x=0\), \(g(0)=-2\).

Answer

The only intersection point is \((0, -2)\).
Rational function graphs 46
Consider \(k(x)=\frac{x^2-4}{x^2-1}\). a) Find the domain and all asymptotes. b) Show that \(k(x)=1-\frac{3}{x^2-1}\) for every \(x\) in the domain. c) Determine the graph's symmetry. d) Find the intervals on which the graph lies above its horizontal asymptote.

Hints

- Factor the denominator and compare leading coefficients. - Combine the terms in the proposed expression over a common denominator. - Compare \(k(-x)\) with \(k(x)\). - Use the sign of the remainder term to compare the graph with the asymptote.

Solution

1. The denominator is zero at \(x=\pm 1\), and the numerator is nonzero there. Thus, the domain is \(\mathbb{R}\setminus\{-1, 1\}\), and the vertical asymptotes are \(x=-1\) and \(x=1\). 2. The numerator and denominator have the same degree, so the horizontal asymptote is \(y=1\). 3. Also, \(1-\frac{3}{x^2-1}=\frac{x^2-1-3}{x^2-1}=\frac{x^2-4}{x^2-1}\). 4. Since \(k(-x)=k(x)\), the graph is symmetric about the y-axis. 5. The graph is above \(y=1\) when \(-\frac{3}{x^2-1}>0\). This occurs when \(x^2-1<0\), or \(-1<x<1\).

Answer

a) Domain: \(\mathbb{R}\setminus\{-1, 1\}\); vertical asymptotes: \(x=-1\), \(x=1\); horizontal asymptote: \(y=1\) b) \(k(x)=1-\frac{3}{x^2-1}\) c) Symmetric about the y-axis d) \((-1, 1)\)
Rational function graphs 47
Consider \(f(x)=\frac{1}{x-2}-\frac{1}{x+2}\), with domain \(\mathbb{R}\setminus\{-2, 2\}\). 1) Show that \(f(x)=\frac{4}{x^2-4}\). 2) Show that the graph is symmetric about the y-axis. 3) Find all vertical and horizontal asymptotes. 4) Find the y-intercept.

Hints

- Use the least common denominator. - Compare \(f(-x)\) with \(f(x)\). - Find denominator zeros and compare degrees. - Substitute \(x=0\) for the y-intercept.

Solution

1. Use the common denominator \((x-2)(x+2)\): \(f(x)=\frac{x+2-(x-2)}{(x-2)(x+2)}=\frac{4}{x^2-4}\). 2. Since \(f(-x)=\frac{4}{(-x)^2-4}=f(x)\), the graph is symmetric about the y-axis. 3. The denominator is zero at \(x=-2\) and \(x=2\), so these are vertical asymptotes. Since the denominator has greater degree than the numerator, the horizontal asymptote is \(y=0\). 4. Evaluate \(f(0)=\frac{4}{-4}=-1\), so the y-intercept is \((0, -1)\).

Answer

1) \(f(x)=\frac{4}{x^2-4}\) 2) Symmetric about the y-axis 3) Vertical asymptotes: \(x=-2\) and \(x=2\); horizontal asymptote: \(y=0\) 4) y-intercept: \((0, -1)\)
Rational function graphs 48
Consider \(g(x)=\frac{1}{x}-\frac{1}{x+4}\), with domain \(\mathbb{R}\setminus\{-4, 0\}\). 1) Show that \(g(x)=\frac{4}{x^2+4x}\). 2) Show that this can also be written as \(g(x)=\frac{4}{(x+2)^2-4}\). 3) Explain why the graph has no x-intercepts. 4) Find all vertical and horizontal asymptotes.

Hints

- Use a common denominator to subtract the fractions. - Complete the square in the quadratic denominator. - A rational expression is zero only when its numerator is zero. - Find denominator zeros and compare degrees.

Solution

1. Use the common denominator \(x(x+4)\): \(g(x)=\frac{x+4-x}{x(x+4)}=\frac{4}{x^2+4x}\). 2. Since \((x+2)^2-4=x^2+4x\), the second form is equivalent. 3. A rational expression equals \(0\) only when its numerator is \(0\). The numerator is the nonzero constant \(4\), so there are no x-intercepts. 4. The denominator is zero at \(x=-4\) and \(x=0\), so these are vertical asymptotes. Since the denominator has greater degree than the numerator, the horizontal asymptote is \(y=0\).

Answer

1) \(g(x)=\frac{4}{x^2+4x}\) 2) \(g(x)=\frac{4}{(x+2)^2-4}\) 3) No x-intercepts 4) Vertical asymptotes: \(x=-4\) and \(x=0\); horizontal asymptote: \(y=0\)
Rational function graphs 49
Let \(f(x)=\frac{6}{x^2+3}\) and \(g(x)=\frac{18}{(x+2)^2+3}\). 1. Describe how to obtain the graph of \(g\) from the graph of \(f\). 2. The graph of \(f\) is symmetric about the y-axis. Use the transformations to explain why the graph of \(g\) is symmetric about the line \(x=-2\).

Hints

- Compare the outside coefficient and the input in the two rules. - Decide whether a vertical stretch moves a vertical symmetry line. - A horizontal translation moves every vertical feature by the same amount. - Track the location of the original symmetry line.

Solution

1. Multiplying \(f\) by \(3\) gives \(3f(x)=\frac{18}{x^2+3}\), a vertical stretch by a factor of \(3\). 2. Replacing \(x\) with \(x+2\) shifts the graph left \(2\) units, producing \(g(x)=\frac{18}{(x+2)^2+3}\). 3. A vertical stretch does not move a vertical line of symmetry, so the symmetry line remains \(x=0\) after the stretch. 4. Shifting the graph left \(2\) units moves the symmetry line from \(x=0\) to \(x=-2\).

Answer

1. Vertically stretch by a factor of \(3\), then shift left \(2\) units. 2. The vertical stretch leaves the symmetry line at \(x=0\); the left shift moves it to \(x=-2\).
Rational function graphs 50
Consider \(f(x)=\frac{6-2x}{x+1}\). a) Find the domain and the horizontal and vertical asymptotes. b) Find the x- and y-intercepts. c) Define \(h(x)=f(x)+x\). Find all asymptotes of the graph of \(h\).

Hints

- Find the denominator zero and compare leading coefficients. - Use \(x=0\) for the y-intercept and set the numerator equal to \(0\) for the x-intercept. - Rewrite \(f\) as a constant plus a rational remainder before adding \(x\).

Solution

1. The denominator is zero at \(x=-1\), so the domain is \(\mathbb{R}\setminus\{-1\}\), and the vertical asymptote is \(x=-1\). 2. The numerator and denominator have the same degree, so the horizontal asymptote is \(y=-2\). 3. Evaluate \(f(0)=6\), so the y-intercept is \((0, 6)\). Solve \(6-2x=0\), giving the x-intercept \((3, 0)\). 4. Rewrite \(f(x)=-2+\frac{8}{x+1}\). Then \(h(x)=x-2+\frac{8}{x+1}\). 5. Therefore, \(h\) has vertical asymptote \(x=-1\) and slant asymptote \(y=x-2\).

Answer

a) Domain: \(\mathbb{R}\setminus\{-1\}\); vertical asymptote: \(x=-1\); horizontal asymptote: \(y=-2\) b) x-intercept: \((3, 0)\); y-intercept: \((0, 6)\) c) Vertical asymptote: \(x=-1\); slant asymptote: \(y=x-2\)
Rational function graphs 51
Consider \(f(x)=\frac{2x^2}{x^2+1}\). 1) Show algebraically that the graph is symmetric about the y-axis. 2) Analyze the function as \(x\to\infty\) and give the equation of the horizontal asymptote. 3) Find all x-values for which \(f(x)=1.8\).

Hints

- Compare \(f(-x)\) with \(f(x)\). - Divide the numerator and denominator by \(x^2\). - Clear the denominator and solve the resulting quadratic equation.

Solution

1. \(f(-x)=\frac{2(-x)^2}{(-x)^2+1}=f(x)\), so the graph is symmetric about the y-axis. 2. Divide by \(x^2\) for nonzero \(x\): \(f(x)=\frac{2}{1+\frac{1}{x^2}}\). As \(x\) becomes very large, the denominator approaches \(1\), so the function approaches \(2\). The horizontal asymptote is \(y=2\). 3. Solve \(\frac{2x^2}{x^2+1}=1.8\). This gives \(2x^2=1.8x^2+1.8\), so \(0.2x^2=1.8\), \(x^2=9\), and \(x=\pm 3\).

Answer

1) Symmetric about the y-axis 2) \(f(x)\to 2\) as \(x\to\infty\); horizontal asymptote: \(y=2\) 3) \(x=-3\) and \(x=3\)
Rational function graphs 52
Show algebraically that the range of \(g(x)=\frac{x^2-4}{x^2+2}\) is \([-2, 1)\).

Hints

- Rewrite the numerator using the denominator. - Determine the possible values of \(x^2+2\). - Track which endpoint values are reached and which are only approached.

Solution

1. Rewrite the function: \(g(x)=\frac{x^2+2-6}{x^2+2}=1-\frac{6}{x^2+2}\). 2. Since \(x^2\ge0\), the denominator \(x^2+2\) takes all values in \([2, \infty)\). 3. Therefore, \(\frac{6}{x^2+2}\) takes all values in \((0, 3]\). The value \(3\) occurs at \(x=0\), while \(0\) is approached but never reached. 4. Subtracting these values from \(1\) gives \(-2\le g(x)<1\). Hence, the range is \([-2, 1)\).

Answer

\([-2, 1)\)
Rational function graphs 53
Find all x-intercepts of each rational function. Account for each function's domain. a) \(f(x)=\frac{x^4-5x^3}{x^2+4}\) b) \(g(x)=\frac{x^2-7x+10}{x-2}\) c) \(h(x)=\frac{x^4-17x^2+16}{x^2+1}\)

Hints

- A rational function equals zero when its numerator is zero and its denominator is nonzero. - Check the domain before accepting numerator zeros. - In part c, notice that the numerator contains only even powers. Look for a factorization in terms of \(x^2\). - Factor each numerator completely before deciding which candidate zeros survive the domain check.

Solution

1. For part a, the denominator is positive for every real \(x\). Factor the numerator: \(x^4-5x^3=x^3(x-5)\). The x-intercepts are \((0,0)\) and \((5,0)\). 2. For part b, \(x=2\) is excluded from the domain. Factor the numerator: \(x^2-7x+10=(x-2)(x-5)\). The candidate \(x=2\) is excluded, so the only x-intercept is \((5,0)\). 3. For part c, the denominator is positive for every real \(x\). The numerator contains only even powers: \(x^4-17x^2+16=(x^2-1)(x^2-16)\). Therefore, \(x=\pm1\) or \(x=\pm4\).

Answer

a) \((0,0)\) and \((5,0)\) b) \((5,0)\) c) \((-4,0)\), \((-1,0)\), \((1,0)\), and \((4,0)\)
Rational function graphs 54
The graphs of two functions intersect at certain points. The functions are \(f(x)=\frac{10}{x-3}\) and \(g(x)=x\). Find the coordinates of all intersection points algebraically.

Hints

- Set the two function expressions equal. - Clear the denominator, while keeping the excluded value in mind. - After finding each x-value, substitute it into either function to find the corresponding y-value. - Check that each x-value is in the domain.

Solution

1. Set the function values equal: \(\frac{10}{x-3}=x\), with \(x\neq 3\). 2. Multiply by \(x-3\): \(10=x(x-3)=x^2-3x\). 3. Rewrite in standard form: \(x^2-3x-10=0\). 4. Factor: \((x-5)(x+2)=0\), so \(x=5\) or \(x=-2\). 5. Since \(g(x)=x\), the corresponding y-values are \(5\) and \(-2\). Both x-values are in the domain of \(f\).

Answer

The intersection points are \((5, 5)\) and \((-2, -2)\).
Rational function graphs 55
Let \(f(x)=\frac{x^2-4}{x^2-1}\). Find the domain and range of \(f\). Use the behavior near excluded values and as \(x\to\pm\infty\) to support your answer.

Hints

- Find the zeros of the denominator. - Rewrite the function as a constant plus a rational term. - Analyze the cases \(|x|>1\) and \(|x|<1\) separately. - Check the behavior near the excluded values and at infinity.

Solution

1. The denominator is zero at \(x=-1\) and \(x=1\), so the domain is \(\mathbb{R}\setminus\{-1, 1\}\). 2. Rewrite the function as \(f(x)=1-\frac{3}{x^2-1}\). For \(|x|>1\), the denominator \(x^2-1\) is positive, so \(f(x)<1\). The function approaches \(1\) as \(x\to\pm\infty\) and approaches \(-\infty\) from the outer sides of the vertical asymptotes. Thus, this part of the domain produces \((-\infty, 1)\). 3. For \(|x|<1\), write \(f(x)=1+\frac{3}{1-x^2}\). Since \(0<1-x^2\leq 1\), \(\frac{3}{1-x^2}\geq 3\), so \(f(x)\geq 4\). 4. The minimum value \(4\) occurs at \(x=0\), and \(f(x)\to\infty\) as \(x\to-1^+\) or \(x\to 1^-\). Therefore, the inner interval produces \([4, \infty)\). 5. Combining the two parts gives the range \((-\infty, 1)\cup[4, \infty)\).

Answer

Domain: \(\mathbb{R}\setminus\{-1, 1\}\) Range: \((-\infty, 1)\cup[4, \infty)\)
Rational function graphs 56
Let \(f(x)=\frac{8}{x^2-2x+5}\). Show that the graph is symmetric about the vertical line \(x=1\).

Hints

- Complete the square in the denominator. - Compare the function values at \(1+h\) and \(1-h\). - Use the fact that \((-h)^2=h^2\).

Solution

1. Complete the square in the denominator: \(x^2-2x+5=(x-1)^2+4\). Thus, \(f(x)=\frac{8}{(x-1)^2+4}\). 2. To verify the symmetry algebraically, compare inputs equally far from \(1\): \(f(1+h)=\frac{8}{h^2+4}\) and \(f(1-h)=\frac{8}{(-h)^2+4}=\frac{8}{h^2+4}\). 3. Since \(f(1+h)=f(1-h)\) for every real \(h\), the graph is symmetric about \(x=1\).

Answer

\(f(1+h)=f(1-h)=\frac{8}{h^2+4}\) for every real \(h\), so the graph is symmetric about \(x=1\).
Rational function graphs 57
Let \(f(x)=\frac{x^4-2x^2+5}{x^2}\), where \(x\neq 0\). 1) Rewrite \(f(x)\) as a quadratic function \(p(x)\) plus a fraction \(r(x)\). 2) Describe what happens to the vertical distance between the graphs of \(f\) and \(p\) as \(\lvert x\rvert\) becomes very large. 3) Is the graph of \(f\) above or below the graph of \(p\) on its domain? Explain.

Hints

- Divide each numerator term by the denominator. - Compare the two function values at the same allowed input. - How do the size and sign of the remaining fraction change when \(\lvert x\rvert\) grows?

Solution

1. Divide each numerator term by \(x^2\): \(f(x)=x^2-2+\frac{5}{x^2}\). Thus, \(p(x)=x^2-2\) and \(r(x)=\frac{5}{x^2}\). 2. The vertical distance between the graphs is \(\lvert f(x)-p(x)\rvert=\frac{5}{x^2}\). As \(\lvert x\rvert\) grows, the denominator grows and the distance approaches \(0\). 3. For every \(x\neq 0\), \(\frac{5}{x^2}>0\). Thus, \(f(x)>p(x)\), so the graph of \(f\) lies above the parabola throughout its domain.

Answer

1) \(p(x)=x^2-2\), \(r(x)=\frac{5}{x^2}\) 2) The vertical distance \(\frac{5}{x^2}\) approaches \(0\) as \(\lvert x\rvert\) becomes very large. 3) The graph of \(f\) lies above the graph of \(p\) for every \(x\neq 0\).
Rational function graphs 58
Consider the family \(f_k(x)=\frac{kx^2+6x}{x-3}\), where \(k\in\mathbb{R}\). a) Find \(k\) so that the graph has a hole at \(x=3\). b) For \(k=1\), find the slant asymptote. c) Find a value of \(k\) for which the graph has a horizontal asymptote, and give its equation.

Hints

- A hole requires a common numerator and denominator zero. - Use polynomial division for the slant asymptote. - Determine which parameter value removes the quadratic term.

Solution

1. For \(x=3\) to be a hole, the numerator must also be zero there: \(9k+18=0\). Thus, \(k=-2\). 2. For \(k=1\), divide \(x^2+6x\) by \(x-3\): \(f_1(x)=x+9+\frac{27}{x-3}\). Therefore, the slant asymptote is \(y=x+9\). 3. A horizontal asymptote is possible when the quadratic numerator term disappears, so set \(k=0\). 4. Then \(f_0(x)=\frac{6x}{x-3}\). The numerator and denominator have the same degree, so the horizontal asymptote is \(y=6\).

Answer

a) \(k=-2\) b) \(y=x+9\) c) For \(k=0\), the horizontal asymptote is \(y=6\).
Rational function graphs 59
Match graphs a, b, and c to the correct functions. One function is not used. Explain each match using asymptotes or intercepts. 1. \(f_1(x)=\frac{x+2}{x-1}\) 2. \(f_2(x)=-\frac{x}{x+2}\) 3. \(f_3(x)=\frac{1}{(x-1)^2}\) 4. \(f_4(x)=\frac{x-2}{x+1}\)
Figure for problem 532480

Hints

- Compare the vertical asymptotes first. - Which curve stays above the x-axis on both sides of its vertical asymptote? - Use an intercept or a horizontal asymptote to distinguish the remaining two curves.

Solution

1. Graph a has vertical asymptote \(x=1\), horizontal asymptote \(y=1\), and x-intercept \((-2, 0)\), matching \(f_1\). 2. Graph b has vertical asymptote \(x=-2\), horizontal asymptote \(y=-1\), and x-intercept \((0, 0)\), matching \(f_2\). 3. Graph c has vertical asymptote \(x=1\), horizontal asymptote \(y=0\), and stays above the x-axis, matching \(f_3\). 4. Function \(f_4\) is unused. It has vertical asymptote \(x=-1\) and x-intercept \((2, 0)\).

Answer

Graph a: \(f_1\); graph b: \(f_2\); graph c: \(f_3\); unused: \(f_4\).
Rational function graphs 60
The graphs are labeled \(g_1\) and \(g_2\). The functions are \(f(x)=\frac{2x+4}{x-1}\) and \(g(x)=\frac{x-3}{x+2}\). a) Match the graphs to the functions. Explain using x-intercepts and vertical asymptotes. b) Find the vertical and horizontal asymptotes of each function. c) Give the domain and range of each function.
Figure for problem 532481

Hints

- Compare each function's numerator zero with the x-intercepts on the graph. - Find which x-value makes each denominator zero. - Rewrite each function as a constant plus a fraction to determine the horizontal asymptote and possible output restrictions.

Solution

1. Function \(f\) has x-intercept \((-2, 0)\) and vertical asymptote \(x=1\), matching \(g_1\). Function \(g\) has x-intercept \((3, 0)\) and vertical asymptote \(x=-2\), matching \(g_2\). 2. Rewrite \(f(x)=2+\frac{6}{x-1}\). Its vertical asymptote is \(x=1\), and its horizontal asymptote is \(y=2\). 3. Rewrite \(g(x)=1-\frac{5}{x+2}\). Its vertical asymptote is \(x=-2\), and its horizontal asymptote is \(y=1\). 4. The domain of \(f\) excludes \(x=1\), and its range excludes \(y=2\). The domain of \(g\) excludes \(x=-2\), and its range excludes \(y=1\).

Answer

a) \(g_1\) is \(f\); \(g_2\) is \(g\). b) For \(f\): \(x=1\), \(y=2\). For \(g\): \(x=-2\), \(y=1\). c) Domain of \(f\): \(\mathbb{R}\setminus\{1\}\); range of \(f\): \(\mathbb{R}\setminus\{2\}\). Domain of \(g\): \(\mathbb{R}\setminus\{-2\}\); range of \(g\): \(\mathbb{R}\setminus\{1\}\).
Rational function graphs 61
Let \(h(x)=\frac{2}{x}\) and \(g(x)=4-x^2\). a) Which real input is not allowed for \(h\)? Describe what happens to \(h(x)\) near that input from each side. b) Estimate the x-coordinates of all intersections of \(h\) and \(g\) from the graph, to the nearest tenth. c) Write an equation for the intersections and show that clearing its denominator gives \(x^3-4x+2=0\).
Figure for problem 532482

Hints

- What does the denominator of the rational function tell you about its graph? - Look for every place where the two curves cross, not only where they meet an axis. - Before multiplying an equation by a variable, what must be true about that variable?

Solution

1. The denominator of \(h\) is zero at \(x=0\), so \(x=0\) is not allowed. As \(x\) approaches \(0\) from the positive side, \(2/x\) grows large and positive; from the negative side, it becomes large and negative. 2. The graph has three intersections, at about \(x=-2.2\), \(x=0.5\), and \(x=1.7\). 3. Set the function values equal: \(\frac{2}{x}=4-x^2\), with \(x\ne0\). 4. Multiply by nonzero \(x\): \(2=4x-x^3\). Rearranging gives \(x^3-4x+2=0\).

Answer

a) \(x=0\). From the right, \(h(x)\) grows positive without bound; from the left, it becomes negative without bound. b) Approximately \(x=-2.2\), \(x=0.5\), and \(x=1.7\). c) \(\frac{2}{x}=4-x^2\), with \(x\ne0\); clearing the denominator gives \(x^3-4x+2=0\).
Rational function graphs 62
Let \(f(x)=1-\frac{4}{x^2-1}\). a) Find the domain and all vertical and horizontal asymptotes. b) Find the x-intercepts. c) Which of the four displayed graphs, \(g_1\), \(g_2\), \(g_3\), or \(g_4\), represents \(f\)? Explain.
Figure for problem 532484

Hints

- Which inputs make the denominator zero? - Compare the behavior of the fraction for large positive and negative inputs. - Find the zeros algebraically, then use them to distinguish curves with similar asymptotes.

Solution

1. The denominator is zero at \(x=-1\) and \(x=1\), so the domain excludes these values. 2. The numerator of the fractional term is nonzero, giving vertical asymptotes \(x=-1\) and \(x=1\). 3. For large positive or negative \(x\), the fraction approaches zero, so the horizontal asymptote is \(y=1\). 4. Set \(1-\frac{4}{x^2-1}=0\). Then \(x^2-1=4\), so the zeros are \(x=\pm\sqrt{5}\). 5. Only graph \(g_1\) has these asymptotes and zeros. It also passes through \((0, 5)\), as required by the formula.

Answer

a) Domain: \(\mathbb{R}\setminus\{-1,1\}\); vertical asymptotes: \(x=-1\) and \(x=1\); horizontal asymptote: \(y=1\). b) \((-\sqrt{5}, 0)\) and \((\sqrt{5}, 0)\). c) \(g_1\).
Rational function graphs 63
Compare panels a) and b). a) Read the vertical and horizontal asymptotes of each graph. b) Near each vertical asymptote, describe whether the outputs become very large positive or very large negative on each side. c) Match each graph to one of the functions. Explain your choices. \(t_1(x)=\frac{x+1}{x-1}\) \(t_2(x)=\frac{1}{x-1}+1\) \(t_3(x)=-\frac{1}{(x+2)^2}+2\) \(t_4(x)=\frac{1}{(x+2)^2}+2\)
Figure for problem 532485

Hints

- Read which vertical and horizontal lines each curve approaches. - Examine the branches very close to, but not at, their vertical asymptotes. - Compare the first two formulas using an intercept, then compare the last two using the direction of their branches.

Solution

1. Panel a) has vertical asymptote \(x=1\) and horizontal asymptote \(y=1\). Near \(x=1\), the outputs become very large negative from the left and very large positive from the right. 2. Panel b) has vertical asymptote \(x=-2\) and horizontal asymptote \(y=2\). Near \(x=-2\), the outputs become very large negative from both sides. 3. Panel a) matches \(t_1\) or \(t_2\) by its asymptotes. Its y-intercept is \((0,-1)\); since \(t_1(0)=-1\) and \(t_2(0)=0\), it matches \(t_1\). 4. Panel b) matches \(t_3\) or \(t_4\) by its asymptotes. Since it drops on both sides of \(x=-2\), it matches \(t_3\).

Answer

a) Panel a): \(x=1\), \(y=1\). Panel b): \(x=-2\), \(y=2\). b) Panel a): negative on the left, positive on the right near \(x=1\). Panel b): negative on both sides near \(x=-2\); each branch falls without bound. c) Panel a): \(t_1\); panel b): \(t_3\).
Rational function graphs 64
Let \(g(x)=\frac{3x^2-12}{x^2+4}\). The graph is shown. a) Show algebraically that the graph is symmetric about the y-axis. b) Describe the end behavior and find the horizontal asymptote. c) Find all x-values for which \(g(x)=2.4\).
Figure for problem 532492

Hints

- What happens to the function rule when you replace \(x\) with \(-x\)? - Can you rewrite the numerator using a multiple of the denominator? - To find the requested input values, set the function equal to \(2.4\) and clear the denominator.

Solution

1. Since \(g(-x)=\frac{3(-x)^2-12}{(-x)^2+4}=g(x)\), the graph is symmetric about the y-axis. 2. Rewrite \(g(x)=3-\frac{24}{x^2+4}\). For large positive or negative \(x\), the fraction gets close to zero, so the graph approaches \(y=3\) at both ends. 3. Set \(\frac{3x^2-12}{x^2+4}=2.4\). Multiplying by \(x^2+4\), which is always positive, gives \(3x^2-12=2.4x^2+9.6\). 4. Then \(0.6x^2=21.6\), so \(x^2=36\) and \(x=-6\) or \(x=6\).

Answer

a) \(g(-x)=g(x)\), so the graph is symmetric about the y-axis. b) The outputs approach \(3\) at both ends; horizontal asymptote: \(y=3\). c) \(x=-6\) and \(x=6\).
Rational function graphs 65
Let \(f(x)=\frac{x^2-x-2}{x^2-4}\) and \(g(x)=\frac{2x^2-4x}{x^2-x-2}\). a) Find each domain and all vertical and horizontal asymptotes. b) Find the coordinates of any holes. c) Match each function to panel a) or b). Explain using graph features.
Figure for problem 532494

Hints

- Factor each numerator and denominator before simplifying. - Keep the original excluded inputs even when a factor cancels. - Substitute an excluded input into the simplified expression to locate its hole. - Compare the remaining asymptotes and hole coordinates with the graphs.

Solution

1. Factor \(f(x)=\frac{(x-2)(x+1)}{(x-2)(x+2)}\). Its domain excludes \(-2\) and \(2\), and it agrees with \(\frac{x+1}{x+2}\) on the domain. Thus, the vertical asymptote is \(x=-2\), and the horizontal asymptote is \(y=1\). 2. The canceled factor leaves a hole at \(x=2\), where the simplified expression equals \(\frac{2+1}{2+2}=\frac{3}{4}\). 3. Factor \(g(x)=\frac{2x(x-2)}{(x-2)(x+1)}\). Its domain excludes \(-1\) and \(2\), and it agrees with \(\frac{2x}{x+1}\) on the domain. The vertical asymptote is \(x=-1\) and the horizontal asymptote is \(y=2\). 4. The canceled factor leaves a hole at \(x=2\), where the simplified expression equals \(\frac{4}{3}\). 5. Panel a) has \(f\)'s asymptotes and hole; panel b) has \(g\)'s asymptotes and hole.

Answer

a) Domain of \(f\): \(\mathbb{R}\setminus\{-2,2\}\); asymptotes \(x=-2\), \(y=1\). Domain of \(g\): \(\mathbb{R}\setminus\{-1,2\}\); asymptotes \(x=-1\), \(y=2\). b) Hole in \(f\): \(\left(2,\frac{3}{4}\right)\). Hole in \(g\): \(\left(2,\frac{4}{3}\right)\). c) Panel a): \(f\); panel b): \(g\).
Rational function graphs 66
The graph shows a function \(g\). Define \(f(x)=\frac{1}{g(x)}\) wherever this is defined. Decide whether each statement is true or false. Explain your decisions. 1) The domain of \(f\) is \(\mathbb{R}\setminus\{-2,2\}\). 2) The graph of \(f\) has horizontal asymptote \(y=0\). 3) As \(x\) approaches \(2\) from the right, \(f(x)\) becomes very large and negative. 4) The graph of \(f\) is symmetric about the y-axis.
Figure for problem 532639

Hints

- When is a reciprocal undefined? - What happens to \(\frac{1}{t}\) as positive \(t\) becomes very large? - Check whether the graphed values just to the right of \(x=2\) are positive or negative. - If two input values give the same output for \(g\), what happens after you take their reciprocals?

Solution

1. Statement 1 is true. The graph shows that \(g(x)=0\) at \(x=-2\) and \(x=2\), so \(f\) is undefined at those inputs. 2. Statement 2 is true. As \(x\) becomes very large positive or negative, \(g(x)\) becomes very large positive, and its reciprocal approaches zero. 3. Statement 3 is false. Just to the right of \(x=2\), \(g(x)\) is positive and approaches zero, so \(f(x)\) becomes very large positive. 4. Statement 4 is true. The graph shows \(g(-x)=g(x)\). Hence \(f(-x)=\frac{1}{g(-x)}=\frac{1}{g(x)}=f(x)\) wherever defined.

Answer

1) True. 2) True. 3) False; \(f(x)\) becomes very large positive when \(x\) approaches \(2\) from the right. 4) True.
Rational function graphs 67
Match each function to Graph 1, Graph 2, or Graph 3. Explain each choice using asymptotes, symmetry, or intercepts. \(f(x)=\frac{2x-4}{x-1}\) \(g(x)=\frac{2x^2}{x^2-1}\) \(h(x)=\frac{2}{x^2+1}\)
Figure for problem 532675

Hints

- How many vertical asymptotes does each function have? - Compare the horizontal asymptotes and intercepts. - Which function has the same output for \(x\) and \(-x\)?

Solution

1. The denominator of \(h\) is always positive, so its graph has no vertical asymptotes. Its y-intercept is \((0,2)\) and its horizontal asymptote is \(y=0\). Thus, \(h\) matches Graph 1. 2. Function \(f\) has vertical asymptote \(x=1\), horizontal asymptote \(y=2\), and x-intercept \((2,0)\), matching Graph 2. 3. Function \(g\) has vertical asymptotes \(x=-1\) and \(x=1\), horizontal asymptote \(y=2\), and passes through \((0,0)\). It is also even because \(g(-x)=g(x)\), matching Graph 3.

Answer

\(f\): Graph 2; \(g\): Graph 3; \(h\): Graph 1.
Rational function graphs 68
Let \(f(x)=x\) and \(g(x)=\frac{2}{x}\). Match the three plotted graphs to these functions: \(s(x)=f(x)+g(x)\), \(d_1(x)=f(x)-g(x)\), and \(d_2(x)=g(x)-f(x)\). Give the letter of each panel and explain your choices using zeros or whether the graphs rise or fall on the right.
Figure for problem 533590

Hints

- Rewrite the sum and the two differences as single fractions. - Which numerator can never be zero for a real input? - How does changing the sign of every output affect the graph? - Try one positive input in each difference to tell their graphs apart.

Solution

1. Combine the sum: \(s(x)=x+\frac{2}{x}=\frac{x^2+2}{x}\), for \(x\ne0\). It has no real zeros because \(x^2+2>0\). This matches panel b). 2. The first difference is \(d_1(x)=x-\frac{2}{x}=\frac{x^2-2}{x}\), which has zeros \(x=\pm\sqrt{2}\). For large positive \(x\), the graph rises. This matches panel c). 3. The second difference is \(d_2(x)=\frac{2}{x}-x=-d_1(x)\). It has the same zeros as \(d_1\), but its graph is reflected across the x-axis and falls for large positive \(x\). This matches panel a).

Answer

a) \(d_2(x)=g(x)-f(x)\); it falls on the right and has zeros \(\pm\sqrt{2}\). b) \(s(x)=f(x)+g(x)\); it has no real zeros. c) \(d_1(x)=f(x)-g(x)\); it rises on the right and has zeros \(\pm\sqrt{2}\).
Rational function graphs 69
Leon studies the graph of \(f(x)=8-\frac{40}{x^2+5}+0.00001x^4\). He claims, “The graph seems to level off near \(y=8\), so the function will approach \(8\) as \(x\) keeps growing.” Is Leon correct? Explain which part of the function rule determines the actual end behavior.
Figure for problem 534029

Hints

- Consider what happens to the fraction when \(x^2+5\) becomes very large. - Does a small positive coefficient prevent \(x^4\) from becoming large? - Compare what you can see in the window with the behavior for much larger inputs.

Solution

1. For large positive \(x\), the fraction \(-\frac{40}{x^2+5}\) gets closer to \(0\). 2. However, the term \(0.00001x^4\) grows without bound, even though its coefficient is small. 3. The positive fourth-power term eventually dominates the constant and rational terms. Thus, \(f(x)\to\infty\) as \(x\to\infty\). 4. Leon's claim is false. The limited viewing window makes the graph appear to level off before its rapid increase becomes visible.

Answer

Leon is incorrect. \(f(x)\to\infty\) as \(x\to\infty\) because the positive fourth-power term eventually dominates.
Rational function graphs 70
The graph of \(h(x)=\frac{2}{x^2-6x+10}\) appears to have a vertical line of symmetry. a) Use the graph to identify the equation of the line of symmetry. b) Prove the symmetry algebraically by showing \(h(x_0-a)=h(x_0+a)\) for every real \(a\), where \(x_0\) is your answer from part a.
Figure for problem 534040

Hints

- Look for the x-coordinate of the graph’s highest point. - Substitute inputs the same distance to the left and right of that x-value. - Expand and simplify each denominator.

Solution

1. The graph reaches its maximum at \(x=3\) and appears mirrored across that vertical line, so \(x_0=3\). 2. Evaluate the two symmetric inputs: \(h(3-a)=\frac{2}{(3-a)^2-6(3-a)+10}=\frac{2}{a^2+1}\). 3. Similarly, \(h(3+a)=\frac{2}{(3+a)^2-6(3+a)+10}=\frac{2}{a^2+1}\). 4. Therefore, \(h(3-a)=h(3+a)\) for every real \(a\), proving symmetry about \(x=3\).

Answer

a) \(x=3\) b) Both \(h(3-a)\) and \(h(3+a)\) simplify to \(\frac{2}{a^2+1}\), so the graph is symmetric about \(x=3\).
Rational function graphs 71
The blue graph is \(f(x)=\frac{4}{x^2+1}\). The red graph has the form \(g(x)=f(b(x+c))\), where \(b>0\). Explain how \(b\) and \(c\) affect the graph. Use the displayed example to determine \(c\), decide whether \(b>1\) or \(0<b<1\), and find \(b\).
Figure for problem 534064

Hints

- Compare the locations of the maximum points. - Compare horizontal distances from each graph center at the same y-value. - Remember that multiplying the input by a number greater than \(1\) makes a graph narrower. - The horizontal scale factor is the reciprocal of \(b\).

Solution

1. The parameter \(c\) controls the horizontal shift. Because the maximum moves from \(x=0\) to \(x=2\), the graph shifts right \(2\) units, so \(c=-2\). 2. The parameter \(b\) controls horizontal scaling. If \(b>1\), the graph is horizontally compressed; if \(0<b<1\), it is horizontally stretched. 3. The blue graph has value \(2\) at \(x=-1\) and \(x=1\), one unit from its center. The red graph has value \(2\) at \(x=0\) and \(x=4\), two units from its center. 4. The horizontal distances doubled, so the horizontal stretch factor is \(2\). Therefore, \(b=\frac{1}{2}\), and \(0<b<1\).

Answer

\(c=-2\), so the graph shifts right \(2\) units; the red graph is wider, so \(0<b<1\), with \(b=\frac{1}{2}\) and horizontal stretch factor \(2\).
Rational function graphs 72
Two rational-function graphs, a and b, are shown. Their rules are \(f(x)=\frac{2x-2}{x+1}\) and \(g(x)=\frac{x^2-1}{x^2-4}\). 1) Match each function to its graph. Explain using asymptotes, symmetry, or intercepts. 2) Describe the end behavior of \(f\) as \(x\) becomes very large positive or negative.
Figure for problem 534109

Hints

- Compare denominator zeros, numerator zeros, and the number of vertical asymptotes. - Which rule is unchanged when \(x\) is replaced by \(-x\)? - Rewrite \(f\) as a constant plus a fraction to determine both end directions.

Solution

1. Function \(f\) has vertical asymptote \(x=-1\), horizontal asymptote \(y=2\), and x-intercept \((1,0)\). These features match graph a. 2. Function \(g\) has vertical asymptotes \(x=-2\) and \(x=2\), horizontal asymptote \(y=1\), and x-intercepts \((-1,0)\) and \((1,0)\). It is symmetric about the y-axis because \(g(-x)=g(x)\), matching graph b. 3. Rewrite \(f(x)=2-\frac{4}{x+1}\). For large positive \(x\), the fraction is small and positive, so \(f(x)\) approaches \(2\) from below. For large negative \(x\), the fraction is small and negative, so \(f(x)\) approaches \(2\) from above. 4. In both directions the graph approaches its horizontal asymptote \(y=2\).

Answer

1) \(f\): graph a; \(g\): graph b. 2) The outputs approach \(2\) at both ends, from below on the right and from above on the left; horizontal asymptote \(y=2\).
Rational function graphs 73
The displayed graphs, a and b, represent \(h(x)=\frac{4}{x^2+1}-1\) and \(k(x)=\frac{x-1}{x-2}\). 1) Match each function to its graph and explain. 2) Find the domain and range of \(h\). 3) Find the x-intercept of \(k\).
Figure for problem 534110

Hints

- Compare symmetry and vertical asymptotes. - How small or large can the fraction in \(h\) become? - For the x-intercept of \(k\), check when its numerator is zero and its denominator is nonzero.

Solution

1. Graph a is symmetric about the y-axis and has no vertical asymptote, so it matches \(h\). Graph b has vertical asymptote \(x=2\), so it matches \(k\). 2. The denominator \(x^2+1\) is always positive, so the domain of \(h\) is \(\mathbb{R}\). 3. The largest value is \(h(0)=3\). For large positive or negative \(x\), the positive fraction approaches zero, so \(h(x)\) approaches \(-1\) from above but never equals \(-1\). Thus, its range is \((-1,3]\). 4. Set the numerator of \(k\) equal to zero: \(x-1=0\), giving the x-intercept \((1,0)\), which is in the domain.

Answer

1) \(h\): graph a; \(k\): graph b. 2) Domain of \(h\): \(\mathbb{R}\); range of \(h\): \((-1,3]\). 3) X-intercept of \(k\): \((1,0)\).
Rational function graphs 74
The coordinate plane shows three rational-function graphs labeled \(f\), \(g\), and \(h\). Match each graph to the correct function. Justify your choices using horizontal asymptotes and x-intercepts. 1. \(f_1(x)=\frac{x-2}{x-3}\) 2. \(f_2(x)=\frac{2x-2}{x-3}\) 3. \(f_3(x)=\frac{x-4}{x-3}\)
Figure for problem 534117

Hints

- First compare the horizontal asymptotes. - Then compare the numerator zeros with the graph x-intercepts. - All three functions have the same vertical asymptote.

Solution

1. All three functions have vertical asymptote \(x=3\). 2. The horizontal asymptotes of \(f_1\) and \(f_3\) are \(y=1\). The horizontal asymptote of \(f_2\) is \(y=2\). Since graph \(g\) approaches \(y=2\), it matches \(f_2\). Its x-intercept \((1, 0)\) confirms the match. 3. The x-intercept of \(f_1\) is \((2, 0)\), so graph \(f\) matches \(f_1\). 4. The x-intercept of \(f_3\) is \((4, 0)\), so graph \(h\) matches \(f_3\).

Answer

Graph \(f\): \(f_1(x)=\frac{x-2}{x-3}\); graph \(g\): \(f_2(x)=\frac{2x-2}{x-3}\); graph \(h\): \(f_3(x)=\frac{x-4}{x-3}\)
Rational function graphs 75
The figure shows the graphs of two rational functions, \(f\) and \(g\). For each function, determine: 1. The location of the vertical asymptote. 2. Whether the graph changes sign across the vertical asymptote. 3. The equation of the horizontal asymptote.
Figure for problem 534121

Hints

- Locate the \(x\)-value where each graph increases or decreases without bound. - Compare the direction of the two branches on opposite sides of each vertical asymptote. - Identify the horizontal line each graph approaches as \(x\) becomes very large in magnitude.

Solution

1. For \(f\), the graph approaches a vertical line at \(x=-4\). It approaches \(-\infty\) from the left and \(+\infty\) from the right, so it changes sign across the vertical asymptote. As \(|x|\) increases, the graph approaches \(y=-3\). 2. For \(g\), the graph approaches a vertical line at \(x=3\). It approaches \(+\infty\) from both sides, so it does not change sign across the vertical asymptote. As \(|x|\) increases, the graph approaches \(y=1\).

Answer

For \(f\), the vertical asymptote is \(x=-4\), the graph changes sign across it, and the horizontal asymptote is \(y=-3\). For \(g\), the vertical asymptote is \(x=3\), the graph does not change sign across it, and the horizontal asymptote is \(y=1\).
Rational function graphs 76
Consider the rational function \(f(x)=\frac{2x^2}{x^2-9}\). The figure shows part of its graph. 1. Find the domain of \(f\), and determine algebraically whether the graph has symmetry. 2. Write equations for all vertical and horizontal asymptotes. 3. Find the coordinates of all intercepts with the coordinate axes.
Figure for problem 534125

Hints

- Find the x-values that make the denominator zero. - Compare \(f(-x)\) with \(f(x)\). - Compare the degrees and leading coefficients of the numerator and denominator. - A rational expression is zero when its numerator is zero and its denominator is not zero.

Solution

1. The denominator is zero when \(x^2-9=0\), so \(x=-3\) or \(x=3\). Therefore, the domain is \((-\infty, -3)\cup(-3, 3)\cup(3, \infty)\). Also, \(f(-x)=\frac{2(-x)^2}{(-x)^2-9}=\frac{2x^2}{x^2-9}=f(x)\). Thus, \(f\) is even, and its graph is symmetric about the y-axis. 2. The vertical asymptotes are \(x=-3\) and \(x=3\). The numerator and denominator have the same degree, so the horizontal asymptote is the ratio of leading coefficients, \(y=2\). 3. Since \(f(0)=0\), the y-intercept is \((0, 0)\). For x-intercepts, set the numerator equal to zero: \(2x^2=0\), so \(x=0\). Therefore, the only intercept is \((0, 0)\).

Answer

1. Domain: \((-\infty, -3)\cup(-3, 3)\cup(3, \infty)\); \(f\) is even, so the graph is symmetric about the y-axis. 2. Vertical asymptotes: \(x=-3\) and \(x=3\); horizontal asymptote: \(y=2\) 3. The only intercept is \((0, 0)\).
Rational function graphs 77
Let \(f(x)=\frac{x^3-3x^2}{x-3}\) and \(g(x)=\frac{x+1}{x-3}\). Figures 1 and 2 show their graphs. a) Match each function to its graph. Explain why one has a hole at \(x=3\) while the other has a vertical asymptote there. b) Find the coordinates of the hole.
Figure for problem 534127

Hints

- Factor the numerator and check whether a denominator factor cancels. - What happens on a graph when a canceled factor still excludes an input? - Use the simplified expression to find the height of the missing point.

Solution

1. Both expressions are undefined at \(x=3\). 2. Factor \(f(x)=\frac{x^2(x-3)}{x-3}\). For allowed \(x\), this equals \(x^2\), so its graph is a parabola with a hole at \(x=3\); this is Figure 2. 3. At \(x=3\), the numerator of \(g\) equals \(4\), so the denominator factor does not cancel. The graph has a vertical asymptote there and is Figure 1. 4. The hole in \(f\) has the y-coordinate \(3^2=9\), giving \((3,9)\).

Answer

a) Figure 1: \(g\), with vertical asymptote \(x=3\); Figure 2: \(f\), with a hole at \(x=3\). b) \((3,9)\).
Rational function graphs 78
Let \(f(x)=\frac{12}{(x-8)^2+3}\) and \(h(x)=\frac{4}{x^2+3}\). 1) Describe how to transform the graph of \(h\) into the graph of \(f\). 2) Find the maximum point of \(f\) algebraically. 3) Prove that the graph of \(f\) is symmetric about the line \(x=8\).

Hints

- Rewrite \(f\) in terms of \(h\). - A positive fraction with a fixed numerator is largest when its denominator is smallest. - To prove symmetry about \(x=a\), compare \(f(a-z)\) and \(f(a+z)\).

Solution

1. Since \(f(x)=3h(x-8)\), shift the graph of \(h\) right \(8\) units and stretch it vertically by a factor of \(3\). 2. The denominator \((x-8)^2+3\) is minimized when \(x=8\). Then \(f(8)=\frac{12}{3}=4\), so the maximum point is \((8,4)\). 3. For any real number \(z\), \(f(8-z)=\frac{12}{(-z)^2+3}=\frac{12}{z^2+3}\). 4. Also, \(f(8+z)=\frac{12}{z^2+3}\). Therefore, \(f(8-z)=f(8+z)\) for every real \(z\), proving symmetry about \(x=8\).

Answer

1) Shift right \(8\) units and stretch vertically by a factor of \(3\). 2) Maximum point: \((8,4)\) 3) \(f(8-z)=f(8+z)=\frac{12}{z^2+3}\), so the graph is symmetric about \(x=8\).
Rational function graphs 79
Consider the function \(f(x)=1+\frac{2}{1+(x-5)^2}\). Its graph is shown. 1. Describe the transformations that produce the graph of \(f\) from the graph of \(g(x)=\frac{1}{1+x^2}\). 2. Find the equation of the horizontal asymptote of the graph of \(f\). 3. Prove that the graph is symmetric about a vertical line, and write the equation of that line.
Figure for problem 534132

Hints

- Compare the locations and heights of the maximum points. - Determine what happens to the fraction as \(|x|\) becomes large. - Compare \(f(5-h)\) and \(f(5+h)\).

Solution

1. Since \(f(x)=2g(x-5)+1\), translate the graph of \(g\) 5 units right, stretch it vertically by a factor of \(2\), and translate it 1 unit up. 2. As \(x\to\pm\infty\), the fraction \(\frac{2}{1+(x-5)^2}\) approaches \(0\). Therefore, \(f(x)\to1\), so the horizontal asymptote is \(y=1\). 3. For every real number \(h\), \(f(5-h)=1+\frac{2}{1+h^2}=f(5+h)\). Therefore, the graph is symmetric about the line \(x=5\).

Answer

1. Translate 5 units right, stretch vertically by a factor of \(2\), and translate 1 unit up. 2. \(y=1\) 3. The graph is symmetric about \(x=5\).
Rational function graphs 80
The graph of \(g(x)=\frac{2x^2-4}{x^2+1}\) is shown. a) Describe its end behavior as \(x\) becomes very large positive or negative. Give the horizontal asymptote. b) Find all x- and y-intercepts. c) Find all x-values for which \(g(x)=1.4\).
Figure for problem 534136

Hints

- Can you rewrite the numerator as a multiple of the denominator plus a constant? - Find intercepts by evaluating at \(x=0\) or setting the numerator to zero. - To find the stated outputs, clear the denominator, which is always positive.

Solution

1. Rewrite \(g(x)=2-\frac{6}{x^2+1}\). When \(x\) is very large positive or negative, the fraction gets close to zero, so \(g(x)\) approaches \(2\) from below at both ends. The horizontal asymptote is \(y=2\). 2. The y-intercept is \(g(0)=-4\), giving \((0,-4)\). 3. To find x-intercepts, solve \(2x^2-4=0\), giving \(x=\pm\sqrt{2}\) and intercepts \((-\sqrt{2},0)\), \((\sqrt{2},0)\). 4. Solve \(\frac{2x^2-4}{x^2+1}=1.4\): \(2x^2-4=1.4x^2+1.4\), so \(0.6x^2=5.4\) and \(x^2=9\). Thus, \(x=-3\) or \(x=3\).

Answer

a) Both ends approach \(2\) from below; horizontal asymptote \(y=2\). b) Y-intercept: \((0,-4)\); x-intercepts: \((-\sqrt{2},0)\), \((\sqrt{2},0)\). c) \(x=-3\) and \(x=3\).
Rational function graphs 81
Let \(h(x)=\frac{3x}{x+4}\), with domain \(\mathbb{R}\setminus\{-4\}\). Show algebraically that the range is \(\mathbb{R}\setminus\{3\}\).

Hints

- Set the function equal to an arbitrary output \(y\). - Solve the equation for \(x\). - Identify the output that makes the resulting expression undefined. - Verify that the calculated input is never the excluded domain value.

Solution

1. Let \(y=\frac{3x}{x+4}\) and solve for \(x\): \(y(x+4)=3x\). 2. Rearranging gives \(x(y-3)=-4y\), so \(x=\frac{-4y}{y-3}\). 3. This expression is defined for every real \(y\) except \(y=3\). Substituting \(y=3\) into the original equation gives \(3x+12=3x\), a contradiction. 4. For \(y\ne3\), the resulting input can never equal the excluded value \(-4\). Otherwise, \(-4=\frac{-4y}{y-3}\) would imply \(12=0\). 5. Therefore, every real value except \(3\) occurs, and the range is \(\mathbb{R}\setminus\{3\}\).

Answer

\(\mathbb{R}\setminus\{3\}\)
Rational function graphs 82
The figure shows three related graphs labeled p, q, and r. a) Match \(g(x)=\frac{4x}{x^2+1}\) to a graph and justify your choice. b) Find equations for the other two graphs. c) Give one possible family \(f_t(x)\) containing all three graphs.
Figure for problem 534488

Hints

- Use zeros and extrema to identify the unshifted graph. - Determine each horizontal shift. - Replace \(x\) with \(x-t\) to represent a horizontal translation.

Solution

1. The function \(g\) has its only zero at \(x=0\) and a local maximum at \((1, 2)\), so it is graph q. 2. Graph p is shifted \(3\) units left, giving \(\frac{4(x+3)}{(x+3)^2+1}\). 3. Graph r is shifted \(2\) units right, giving \(\frac{4(x-2)}{(x-2)^2+1}\). 4. A family describing horizontal shifts is \(f_t(x)=\frac{4(x-t)}{(x-t)^2+1}\).

Answer

a) Graph q b) p: \(\frac{4(x+3)}{(x+3)^2+1}\); r: \(\frac{4(x-2)}{(x-2)^2+1}\) c) \(f_t(x)=\frac{4(x-t)}{(x-t)^2+1}\)
Rational function graphs 83
A small solar installation has power output \(P(x)=\frac{24}{(x-14)^2+2}\), in kilowatts, from 8:00 a.m. to 8:00 p.m. The input \(x\) is the number of hours after midnight. a) Starting with \(h(x)=\frac{4}{x^2+2}\), describe the transformations that produce the graph of \(P\). Explain why the graph is symmetric about \(x=14\). b) The maximum output is \(12\,\text{kW}\). To the nearest minute, at what afternoon time does output fall to \(25\%\) of its maximum?
Figure for problem 534540

Hints

- Can you write the new output rule using the original function \(h\)? - Find one quarter of the maximum power, then solve for the input time. - The squared equation gives two times. Which one is in the afternoon? - Convert the fraction of an hour into minutes.

Solution

1. Since \(P(x)=6h(x-14)\), shift \(h\) right \(14\) units and stretch vertically by a factor of \(6\). 2. Function \(h\) is even, so the translated graph is symmetric about \(x=14\). 3. The maximum occurs at \(x=14\): \(P(14)=\frac{24}{2}=12\,\text{kW}\). One quarter is \(3\,\text{kW}\). 4. Solve \(\frac{24}{(x-14)^2+2}=3\): \((x-14)^2+2=8\), giving \(x=14\pm\sqrt{6}\). 5. The afternoon input is \(x=14+\sqrt{6}\approx16.449\). The decimal part is approximately \(0.449\cdot60\approx27\) minutes, giving about 4:27 p.m.

Answer

a) Shift right \(14\) units and stretch vertically by \(6\); symmetry line \(x=14\). b) Approximately 4:27 p.m.
Rational function graphs 84
Consider \(g(x)=\frac{3x}{x^2+1}\). The graph is shown. a) Use the function rule to determine the graph's symmetry. b) Read the coordinates of its two local extrema from the graph. c) Find the horizontal asymptote and explain using the degrees of the numerator and denominator.
Figure for problem 534722

Hints

- Compare \(g(-x)\) with \(g(x)\) and \(-g(x)\). - Read where the curve changes from rising to falling or from falling to rising. - Compare the degrees of the numerator and denominator to explain the end behavior.

Solution

1. Since \(g(-x)=\frac{-3x}{x^2+1}=-g(x)\), the function is odd, so its graph is symmetric about the origin. 2. The graph has a local maximum at \((1,1.5)\) and a local minimum at \((-1,-1.5)\). 3. The denominator has a higher degree than the numerator. For large positive or negative inputs, \(\frac{3x}{x^2+1}\) approaches zero. Thus, the horizontal asymptote is \(y=0\).

Answer

a) Symmetric about the origin. b) Local maximum: \((1,1.5)\); local minimum: \((-1,-1.5)\). c) Horizontal asymptote: \(y=0\).
Rational function graphs 85
Match each rational function to the corresponding graph labeled a through d. State the key features you used, such as vertical asymptotes, end behavior, or intercepts. \(g_1(x)=\frac{x^2-1}{x}\) \(g_2(x)=\frac{2}{x^2+1}\) \(g_3(x)=\frac{x-2}{x+2}\) \(g_4(x)=\frac{1}{(x-1)^2}\)
Figure for problem 534840

Hints

- Find the zeros of each denominator to identify possible vertical asymptotes. - Compare the functions’ end behavior to identify horizontal or slant asymptotes. - Find intercepts that distinguish functions with similar asymptotes. - Check whether each graph changes sign across a vertical asymptote.

Solution

1. Graph a matches \(g_1\). It has a vertical asymptote at \(x=0\), x-intercepts at \(x=-1\) and \(x=1\), and slant asymptote \(y=x\). 2. Graph b matches \(g_2\). It is symmetric about the y-axis, has no vertical asymptotes, has a maximum at \((0, 2)\), and approaches \(y=0\). 3. Graph c matches \(g_3\). It has a vertical asymptote at \(x=-2\), an x-intercept at \((2, 0)\), and horizontal asymptote \(y=1\). 4. Graph d matches \(g_4\). It stays above the x-axis and has a vertical asymptote at \(x=1\), approaching positive infinity from both sides.

Answer

\(g_1\to\text{a}\); \(g_2\to\text{b}\); \(g_3\to\text{c}\); \(g_4\to\text{d}\)
Rational function graphs 86
Consider \(h(x)=\frac{x+1}{x-1}\) and \(k(x)=\frac{2x+2}{x+2}\), each on its domain. a) Find the vertical and horizontal asymptotes of both functions. b) Find all intersection points of their graphs.

Hints

- Denominator zeros identify possible vertical asymptotes. - Compare leading coefficients for horizontal asymptotes. - When solving the intersection equation, do not cancel \(x+1\) before considering \(x=-1\). - Check each solution against both domains.

Solution

1. For \(h\), the vertical asymptote is \(x=1\), and the horizontal asymptote is \(y=1\). 2. For \(k\), the vertical asymptote is \(x=-2\), and the horizontal asymptote is \(y=2\). 3. Set the functions equal: \(\frac{x+1}{x-1}=\frac{2(x+1)}{x+2}\). 4. One solution occurs when \(x+1=0\), giving \(x=-1\) and \(y=0\). 5. If \(x+1\neq 0\), cancel it and solve \(\frac{1}{x-1}=\frac{2}{x+2}\). Then \(x+2=2x-2\), so \(x=4\). 6. Evaluate \(h(4)=\frac{5}{3}\).

Answer

a) \(h\): vertical \(x=1\), horizontal \(y=1\); \(k\): vertical \(x=-2\), horizontal \(y=2\) b) \((-1, 0)\) and \(\left(4, \frac{5}{3}\right)\)
Rational function graphs 87
Consider the family \(f_a(x)=\frac{2a}{x+1}\) and the line \(g(x)=x-2\), where \(a\in\mathbb{R}\). Determine the number of intersection points of their graphs for each value of \(a\).

Hints

- Set the two function expressions equal and obtain a quadratic equation in \(x\). - Use the discriminant to classify the number of real roots. - Check whether the excluded value \(x=-1\) appears as a root for any parameter value.

Solution

1. Set the functions equal: \(\frac{2a}{x+1}=x-2\), with \(x\neq-1\). 2. Clear the denominator: \(2a=(x-2)(x+1)=x^2-x-2\). Thus, \(x^2-x-2-2a=0\). 3. The discriminant is \(\Delta=1+4(2+2a)=9+8a\). 4. If \(a<-\frac{9}{8}\), then \(\Delta<0\), so there are no intersections. If \(a=-\frac{9}{8}\), then \(\Delta=0\), so there is one intersection. If \(a>-\frac{9}{8}\), the quadratic has two real roots before domain restrictions are checked. 5. The excluded value \(x=-1\) is a root of the quadratic only when \(a=0\). For \(a=0\), the other root is \(x=2\), so there is one valid intersection. 6. Therefore, there are two intersections when \(a>-\frac{9}{8}\) and \(a\neq 0\).

Answer

If \(a<-\frac{9}{8}\): \(0\) intersection points If \(a=-\frac{9}{8}\) or \(a=0\): \(1\) intersection point If \(a>-\frac{9}{8}\) and \(a\neq 0\): \(2\) intersection points
Rational function graphs 88
Consider \(f_k(x)=\frac{x+k}{x-2}\) and \(g(x)=x-4\), where \(k\in\mathbb{R}\). Find all values of \(k\) for which the graphs have exactly one intersection point.

Hints

- Set the two function expressions equal and clear the denominator. - A quadratic has one repeated real solution when its discriminant is \(0\). - A second possibility occurs when one algebraic solution is excluded from the rational function's domain.

Solution

1. Set the functions equal, with \(x\neq 2\): \(\frac{x+k}{x-2}=x-4\). 2. Clear the denominator to obtain \(x^2-7x+8-k=0\). 3. One intersection occurs when the quadratic has one repeated root. Its discriminant is \(49-4(8-k)=17+4k\). Setting this equal to \(0\) gives \(k=-\frac{17}{4}\). The repeated root is \(x=\frac{7}{2}\), which is valid. 4. One intersection can also occur when the quadratic has two roots but one is the excluded value \(x=2\). Substituting \(x=2\) gives \(k=-2\). 5. For \(k=-2\), the quadratic factors as \((x-2)(x-5)=0\). Only \(x=5\) is valid, so there is exactly one intersection.

Answer

\(k=-\frac{17}{4}\) or \(k=-2\)
Rational function graphs 89
Let \(f(x)=\frac{3x}{x^2-4}\), with domain \(\mathbb{R}\setminus\{-2, 2\}\). Prove that the range of \(f\) is all real numbers.

Hints

- Treat an arbitrary output \(y\) as a fixed number and solve for \(x\). - Separate the case \(y=0\). - Use the discriminant of the resulting quadratic equation. - Check that the solutions cannot equal the excluded inputs.

Solution

1. Let \(y\) be an arbitrary real number and solve \(y=\frac{3x}{x^2-4}\) for \(x\). Clearing the denominator gives \(y(x^2-4)=3x\), or \(yx^2-3x-4y=0\). 2. If \(y=0\), the equation becomes \(-3x=0\), so \(x=0\), which is in the domain. 3. If \(y\ne0\), this is a quadratic equation in \(x\). Its discriminant is \(\Delta=(-3)^2-4\cdot y\cdot(-4y)=9+16y^2>0\). 4. Therefore, the equation has real solutions for every nonzero real \(y\). 5. Neither excluded input can be a solution: substituting \(x=2\) into \(y(x^2-4)=3x\) would give \(0=6\), and substituting \(x=-2\) would give \(0=-6\). 6. Thus, every real \(y\) has at least one allowed preimage, so the range is \(\mathbb{R}\).

Answer

For every \(y\in\mathbb{R}\), the equation \(y=\frac{3x}{x^2-4}\) has an allowed real solution. Therefore, the range is \(\mathbb{R}\).
Rational function graphs 90
Find all zeros of \(f(x)=\frac{x^4-10x^2+9}{x^2-2x-3}\), including the multiplicity of each zero.

Hints

- Determine the original domain before accepting any numerator zeros. - The numerator contains only even powers of \(x\). Look for a factorization built from expressions in \(x^2\). - A rational function equals zero only when its numerator is zero and its denominator is nonzero. - Compare the numerator and denominator factors before deciding which zeros remain.

Solution

1. Factor the denominator: \(x^2-2x-3=(x-3)(x+1)\). Thus, the domain excludes \(x=3\) and \(x=-1\). 2. The numerator contains only even powers. Factor it as a quadratic in \(x^2\): \(x^4-10x^2+9=(x^2-1)(x^2-9)\). 3. Thus the numerator zeros are \(x=\pm1\) and \(x=\pm3\). 4. The values \(x=3\) and \(x=-1\) are excluded from the domain. Factoring the full expression gives \(\frac{(x-3)(x+3)(x-1)(x+1)}{(x-3)(x+1)}=(x+3)(x-1)\) on the original domain. 5. Therefore, the zeros are \(x=-3\) and \(x=1\), each with multiplicity \(1\).

Answer

\(x=-3\) has multiplicity \(1\), and \(x=1\) has multiplicity \(1\).
Rational function graphs 91
Let \(f(x)=\frac{1}{x}+2\), with \(x\neq 0\), and \(g(x)=x^3-x\). Determine the number of intersection points of their graphs.

Hints

- Set the functions equal and clear the denominator. - Look for a difference-of-squares structure in the resulting quartic. - Use discriminants to count the real roots of the quadratic factors. - Check the excluded value.

Solution

1. Set the functions equal: \(\frac{1}{x}+2=x^3-x\), with \(x\neq 0\). 2. Multiply by \(x\): \(1+2x=x^4-x^2\), so \(x^4-x^2-2x-1=0\). 3. Rewrite this as \(x^4-(x+1)^2=0\), then factor the difference of squares: \((x^2-x-1)(x^2+x+1)=0\). 4. The equation \(x^2-x-1=0\) has two real solutions because its discriminant is \(5\). The equation \(x^2+x+1=0\) has no real solutions because its discriminant is \(-3\). 5. Neither real solution is \(0\), so the graphs have exactly two intersection points.

Answer

The graphs have exactly \(2\) intersection points.
Rational function graphs 92
Consider the graph of \(g(x)=\frac{4x^2+50}{x^2+10}-0.00005x^4\). a) Does the graph show any negative outputs? Does that prove \(g(x)>0\) for every real \(x\)? b) What actually happens to \(g(x)\) as \(x\) becomes very large and positive? Explain why the visible graph cannot settle this question.
Figure for problem 534030

Hints

- Check whether every output you can see is above the x-axis. How far does the x-axis extend in the drawing? - Think about the long-term behavior of each part of the formula separately. - Could a smaller coefficient eventually be outweighed by a higher power of x? - Test an input beyond the graph's window to challenge your first impression.

Solution

1. All displayed outputs are positive. A graph drawn over a limited window cannot prove that every output is positive. 2. The numerator and denominator of the rational term have the same degree, so that term approaches \(4\) for large positive \(x\). 3. The term \(-0.00005x^4\) falls without bound and eventually dominates the rational term. Thus, \(g(x)\to-\infty\) as \(x\to\infty\). 4. For example, \(g(50)\approx-308.50\), outside the displayed window. The full graph eventually has negative outputs.

Answer

a) No negative outputs are shown. No, the displayed window does not prove \(g(x)>0\) for every real \(x\). b) \(g(x)\to-\infty\) as \(x\to\infty\). The negative fourth-power term eventually dominates the bounded rational part.
Rational function graphs 93
Let \(g(x)=\frac{3x^2}{x^2-9}\). a) Find all vertical and horizontal asymptotes. b) Determine algebraically whether the graph intersects its horizontal asymptote. c) Use the graph to find the range.
Figure for problem 534115

Hints

- Find the denominator zeros and compare leading coefficients. - Set the function equal to the horizontal-asymptote value. - Use the middle and outer branches separately to determine the range.

Solution

1. The denominator is zero at \(x=-3\) and \(x=3\), so the vertical asymptotes are \(x=-3\) and \(x=3\). 2. The numerator and denominator have the same degree, and the ratio of leading coefficients is \(3\). Thus, the horizontal asymptote is \(y=3\). 3. To test for an intersection, set \(g(x)=3\): \(\frac{3x^2}{x^2-9}=3\). This gives \(3x^2=3x^2-27\), which is impossible. Therefore, the graph does not intersect \(y=3\). 4. On \((-3, 3)\), the graph has a maximum at \((0, 0)\) and approaches \(-\infty\) near both vertical asymptotes, producing all values in \((-\infty, 0]\). 5. On the outer intervals, the graph approaches \(\infty\) near the vertical asymptotes and approaches \(3\) from above as \(|x|\to\infty\), producing \((3, \infty)\). 6. Therefore, the range is \((-\infty, 0]\cup(3, \infty)\).

Answer

a) Vertical asymptotes: \(x=-3\) and \(x=3\); horizontal asymptote: \(y=3\) b) The graph does not intersect \(y=3\). c) \((-\infty, 0]\cup(3, \infty)\)
Rational function graphs 94
Let \(k(x)=\frac{2x^2}{x^2+1}\), with domain \(\mathbb{R}\). Prove that its range is \([0,2)\).

Hints

- Establish a lower bound using the signs of the numerator and denominator. - Rewrite the function as a constant minus a positive fraction. - To prove every value in the interval occurs, set the function equal to an arbitrary \(y\) in that interval and solve for \(x^2\).

Solution

1. Since \(x^2\ge0\) and \(x^2+1>0\), \(k(x)\ge0\). The value \(0\) occurs at \(x=0\). 2. Rewrite the function as \(k(x)=2-\frac{2}{x^2+1}\). The fraction is always positive, so \(k(x)<2\). As \(|x|\to\infty\), the fraction approaches \(0\), so the outputs approach \(2\) without reaching it. 3. To show that every value between the bounds occurs, let \(0\le y<2\). Solving \(y=\frac{2x^2}{x^2+1}\) gives \(x^2=\frac{y}{2-y}\). 4. Because \(\frac{y}{2-y}\ge0\), a real solution exists, for example \(x=\sqrt{\frac{y}{2-y}}\). Thus, every \(y\in[0,2)\) is attained.

Answer

\([0,2)\)

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