College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter 4 - Section 4.3 - Quadratic Functions and Their Properties - 4.3 Assess Your Understanding - Page 299: 30

Answer

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Work Step by Step

Write $f$ in the form $f(x)=a(x-h)^{2}+k$: $\displaystyle \begin{aligned}f(x)&=-2x^{2}+6x+2\displaystyle \\&=-2(x^{2}-3x)+2\\&=-2(x^{2}-3x+\displaystyle \frac{9}{4})+2+2\cdot\frac{9}{4}\\&=-2\displaystyle (x-1.5)^{2}+6.5\end{aligned}$ Let $f_{1}(x)=x^{2}$. Then, $f(x)=-2f_{1}(x-1.5)+6.5$. The graph is obtained from $f_{1}(x)$ by - reflecting about the x-axis $\quad(x,y)\rightarrow(x,-y),$ - stretching by factor 2 $\quad (x,-y)\rightarrow(x,-2y)$ - shifting to the right by $1.5$ units,$\quad (x,-2y)\rightarrow (x+1.5,-2y)$ - and then up by 6.5 units $\quad (x+1.5,-2y+6.5)$ Point by point, $\left[\begin{array}{lll} (x,y) & \rightarrow & (x+1.5,-2y+6.5)\\ & & \\ (0,0) & \rightarrow & (1.5,6.5)\\ (-1,1) & \rightarrow & (0.5,4.5)\\ (1,1) & \rightarrow & (2.5,4.5)\\ (-2,4) & \rightarrow & (-0.5,-1.5)\\ (2,4) & \rightarrow & (3.5,-1.5) \end{array}\right]$
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