The table shows values of a quadratic function \(f\).
<table> <tr><td>\(x\)</td><td>\(-2\)</td><td>\(-1\)</td><td>\(0\)</td><td>\(1\)</td><td>\(2\)</td><td>\(3\)</td></tr> <tr><td>\(f(x)\)</td><td>\(-4\)</td><td>\(2\)</td><td>\(4\)</td><td>\(2\)</td><td>\(-4\)</td><td>\(-14\)</td></tr> </table>
a) Create value tables for \(g(x)=2.5f(x)\) and \(h(x)=-0.5f(x)\).
b) Describe how the graphs of \(g\) and \(h\) are obtained from the graph of \(f\).
c) Find a possible rule for \(f\), then write rules for \(g\) and \(h\).
Hints
- Multiply each given output by the outside scale factor.
- A negative scale factor also reflects the graph across the x-axis.
- Use finite differences to identify the function type.
- An outside factor distributes to every term of the function rule.
Solution
1. Multiply each output by \(2.5\): the values of \(g\) are \(-10, 5, 10, 5, -10, -35\).
2. Multiply each output by \(-0.5\): the values of \(h\) are \(2, -1, -2, -1, 2, 7\).
3. The graph of \(g\) is a vertical stretch of the graph of \(f\) by a factor of \(2.5\). The graph of \(h\) is a vertical compression by a factor of \(0.5\) followed by a reflection across the x-axis.
4. The second differences of the \(f(x)\)-values are constant at \(-4\), so let \(f(x)=ax^2+bx+c\). From \(f(0)=4\), \(c=4\). Since \(f(-1)=f(1)\), \(b=0\). From \(f(1)=2\), \(a+4=2\), so \(a=-2\).
5. Therefore, \(f(x)=-2x^2+4\), \(g(x)=2.5(-2x^2+4)=-5x^2+10\), and \(h(x)=-0.5(-2x^2+4)=x^2-2\).
Answer
a) \(g(x)\)-values: \(-10, 5, 10, 5, -10, -35\)
\(h(x)\)-values: \(2, -1, -2, -1, 2, 7\)
b) \(g\) is a vertical stretch by a factor of \(2.5\). \(h\) is a vertical compression by a factor of \(0.5\) and a reflection across the x-axis.
c) \(f(x)=-2x^2+4\), \(g(x)=-5x^2+10\), and \(h(x)=x^2-2\)