Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 2 - Section 2.2 - Quadratic Functions - Exercise Set - Page 330: 7

Answer

The function of the given graph is\[g\left( x \right)={{x}^{2}}-2x+1\]

Work Step by Step

A quadratic function can be expressed as $f\left( x \right)=a{{x}^{2}}+bx+c$ corresponding to which the graph is a parabola whose vertex is the point $\left( h,k \right)=\left( \frac{-b}{2a},f\left( \frac{-b}{2a} \right) \right)$. If $a>0$ , the parabola opens upward and if $a<0$ then the parabola opens downward. Now, it can be observed that the given parabola has a vertex on $\left( 1,0 \right)$ and opens upwards. Thus, in comparison with the standard equation, the value of $\left( \frac{-b}{2a},f\left( \frac{-b}{2a} \right) \right)$ is: $\left( \frac{-b}{2a},f\left( \frac{-b}{2a} \right) \right)=\left( 1,0 \right)$ This implies, $\begin{align} & \frac{-b}{2a}=1 \\ & b=-2a \end{align}$ and, $f\left( 1 \right)=0$ Putting in the values in the standard form we get: $\begin{align} & f\left( 1 \right)=a{{\left( 1 \right)}^{2}}+b\left( 1 \right)+c \\ & 0=a+b+c \\ & 0=a-2a+c \\ & a=c \end{align}$ Substituting the values of b and c obtained in the standard equation, we obtain: $f\left( x \right)=a{{x}^{2}}-2ax+a$ Where, $a>0$ the parabola opens upwards. The coefficients of ${{x}^{2}}$ and constant $c$ are equal and have opposite in sign to x. This equation is similar to $g\left( x \right)={{x}^{2}}-2x+1$. Therefore, the required equation of the graph is $g\left( x \right)={{x}^{2}}-2x+1$.
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