Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 3 - Linear and Quadratic Functions - Chapter Review - Chapter Test - Page 164: 3

Answer

The $y$-intercept is $1$. The $x$-intercepts are $\dfrac{2-\sqrt 6}{2}$ and $\dfrac{2+\sqrt 6}{2}$.

Work Step by Step

Determine the $y$-intercept by setting $x=0$ then solving the equation for $y$: $y=f(0)=-2(0^2)+4(0)+1=1$ Thus, the $y$-intercept is $1$. Determine the $x$-intercepts by sestting $y$ to $0$ then solving the equation using the quadratic formula $x=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}$. $-2x^2+4x+1=0$ (so $a=-2, b=4,$ and $c=1$) $x=\dfrac{-4\pm\sqrt{4^2-4(-2)(1)}}{2(-2)}=\dfrac{-4\pm\sqrt{24}}{-4}\\ x=\dfrac{-4\pm\sqrt{4\cdot6}}{-4}=\dfrac{-4\pm 2\sqrt 6}{-4}=\dfrac{2\pm \sqrt 6}{2}$ $x_1=\dfrac{2-\sqrt 6}{2}$ $x_2=\dfrac{2+\sqrt 6}{2}$ Thus, the $x$-intercepts are $\dfrac{2-\sqrt 6}{2}$ and $\dfrac{2+\sqrt 6}{2}$.
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