Intermediate Algebra: Connecting Concepts through Application

Published by Brooks Cole
ISBN 10: 0-53449-636-9
ISBN 13: 978-0-53449-636-4

Chapter 4 - Quadratic Functions - 4.5 Solving Equations by Factoring - 4.5 Exercises - Page 361: 66

Answer

$y=-2x^2+12x-10$

Work Step by Step

Recall: The equation of a quadratic function whose vertex is at $(h, k)$ is given by the equation $y=a(x-h)^2+k$ The graph shows that vertex of the function at $(3, 8)$ so we have $h=3$ and $k=8$. Thus, the equation of the function whose graph is given is: $$y=a(x-3)^2+8$$ Since the graph contains the point $(1, 0)$, substitute the $1$ to $x$ and $0$ to $y$ to obtain: \begin{align*} 0&=a(1-3)^2+8\\ 0&=a(-2)^2+8\\ 0&=a(4)+8\\ -8&=4a\\ -2&=a \end{align*} Therefore, the equation of the quadratic function whose gaph is given is: $$y=-2(x-3)^2+8$$ Expand the binomial then simplify to obtain: \begin{align*} y&=-2(x^2-6x+9)+8\\ y&=-2x^2+12x-18+8\\ y&=-2x^2+12x-10 \end{align*}
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