Precalculus (10th Edition)

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

Chapter 2 - Functions and Their Graphs - Chapter Review - Cumulative Review - Page 117: 15

Answer

$x$-intercepts: $\quad-2$ and $2$ $y$-intercept: $\quad-3$; symmetric with the $y$-axis

Work Step by Step

Step $1$. To find the $x$-intercept, set $y=0$ then solve for $x$ to obtain: $$\begin{align*} 3x^2-4y&=12\\ 3x^2-4(0)&=12\\ 3x^2&=12\\ x^2&=4\\ x&=\pm\sqrt{4}\\ x&=\pm2 \end{align*}$$ Thus, the $x$-intercepts are $\pm2$ Step $2$. To find the $y$-intercept, set $x=0$ then solve for $y$ to obtain: $$\begin{align*} 3x^2-4y&=12\\ 3(0^2)-4y&=12\\ -4y&=12\\ y&=-3 \end{align*}$$ Thus, the $y$-intercept is $-3$. Step $3$. To test for symmetry, replace $(x,y)$ with $(x,-y)$ (x-axis symmetry), or $(-x,y)$ (y-axis symmetry), or $(-x,-y)$ (origin symmetry), and see if the equation remain unchanged. Replace $(x, y)$ with $(x, -y)$ to obtain: $\begin{align*} 3x^2-4(-y)&=12\\ 3x^2+4y&=12 \end{align*}$ The equation is different from the original so there is no symmetry with respect to $x$-axis. Replace $(x, y)$ with $(-x, y)$ to obtain: $\begin{align*} 3(-x)^2-4y&=12\\ 3x^2-4y&=12 \end{align*}$ The equation is the same as the original so there is symmetry with respect to $y$-axis. Replace $(x, y)$ with $(-x, -y)$ to obtain: $\begin{align*} 3(-x)^2-4(-y)&=12\\ 3x^2+4y&=12 \end{align*}$ The equation is different from the original so there is no symmetry with resspect to the origin. We can see that the equation has only $y$-axis symmetry.
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