Intermediate Algebra for College Students (7th Edition)

Published by Pearson
ISBN 10: 0-13417-894-7
ISBN 13: 978-0-13417-894-3

Chapter 8 - Test - Page 659: 17

Answer

Vertex: $(1,4)$ $x$-intercepts: $-1$; $3$; $y$-intercept: $-3$

Work Step by Step

Bring the function to the vertex form $f(x)=a(x-h)^2+k$: $$\begin{align*} f(x)&=(x^2-2x+1)-4\\ &=(x^2-2x+1)-4\\ &=(x-1)^2-4. \end{align*}$$ Identify the constants $a$, $h$, $k$: $$\begin{align*} a&=1\\ h&=1\\ k&=-4. \end{align*}$$ Determine the vertex of the function: $$(h,k)=(1,-4).$$ The axis of symmetry is $x=1$. It opens upward because $a>0$. Determine the $x$-intercepts by solving the equation $f(x)=0$: $$\begin{align*} (x-1)^2-4&=0\\ (x-1)^2&=4\\ x-1&=\pm 2\\ x-1=-2&\text{ or }x-1=2\\ x=-1&\text{ or }x=3. \end{align*}$$ The $x$-intercepts are $-1$ and $3$. Determine the $y$-intercept: $$f(0)=(0-1)^2-4=-3.$$ The $y$-intercept is $-3$. We plot the vertex $(1,-4)$ and the intercept points $(-1,0)$, $(3,0)$ and $(0,-3)$, then join them to sketch the graph of the function:
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