Let \(f(x)=\frac{x-2}{x+1}\).
a) Find the domain, x-intercept, vertical asymptote, and horizontal asymptote of \(f\).
b) Rewrite the function in the form \(f(x)=a+\frac{b}{x+1}\). Find \(a\) and \(b\).
c) Describe how to transform the graph of \(y=\frac{1}{x}\) to obtain the graph of \(f\).
Hints
- Find the value that makes the denominator zero.
- Compare the degrees and leading coefficients to find the horizontal asymptote.
- Rewrite the numerator using \(x+1\).
- In the form \(a\frac{1}{x-h}+k\), identify the reflection, stretch, and translations.
Solution
1. The denominator is zero at \(x=-1\), so the domain is \(\mathbb{R}\setminus\{-1\}\).
2. The numerator is zero at \(x=2\), so the x-intercept is \((2, 0)\).
3. Since the denominator is zero and the numerator is nonzero at \(x=-1\), the vertical asymptote is \(x=-1\). The numerator and denominator have the same degree, so the horizontal asymptote is the ratio of the leading coefficients: \(y=1\).
4. Rewrite the numerator as \(x-2=(x+1)-3\): \(f(x)=\frac{x+1-3}{x+1}=1-\frac{3}{x+1}\). Thus, \(a=1\) and \(b=-3\).
5. Starting with \(y=\frac{1}{x}\), stretch vertically by a factor of \(3\), reflect across the x-axis, shift left \(1\) unit, and shift up \(1\) unit.
Answer
a) Domain: \(\mathbb{R}\setminus\{-1\}\); x-intercept: \((2, 0)\); vertical asymptote: \(x=-1\); horizontal asymptote: \(y=1\)
b) \(f(x)=1-\frac{3}{x+1}\), so \(a=1\) and \(b=-3\).
c) Stretch vertically by a factor of \(3\), reflect across the x-axis, shift left \(1\) unit, and shift up \(1\) unit.