Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 7 - Algebra: Graphs, Functions, and Linear Systems - 7.6 Modeling Data: Exponential, Logarithmic, and Quadratic Functions - Exercise Set 7.6 - Page 475: 28

Answer

See below:

Work Step by Step

Consider the quadratic function: $f\left( x \right)=-3{{x}^{2}}+6x-2$ Now, consider the equation of the vertex for the quadratic formula. $x=\frac{-b}{2a}$ Substitute the values in the above equation. $\begin{align} & x=\frac{-6}{2\left( -3 \right)} \\ & =1 \end{align}$ This shows that the vertex is located, when x is equal to1. Substitute, x as 1 in the provided equation: $\begin{align} & y=-3{{\left( 1 \right)}^{2}}+6\left( 1 \right)-2 \\ & =-3+6-2 \\ & =1 \end{align}$ This shows that the vertex occurs at the coordinate, $\left( 1,1 \right)$. Now, substitute x as 0 in the above function to calculate the y intercept. $\begin{align} & y=-3{{\left( 0 \right)}^{2}}+6\left( 0 \right)-2 \\ & =-2 \end{align}$ This shows that the y intercept occurs at the coordinate, $\left( 0,-2 \right)$. Now, substitute y as 0 in the above function to calculate the x intercept. $0=-3{{x}^{2}}+6x-2$ It is further solved using the quadratic function. $\begin{align} & x=\frac{-6\pm \sqrt{{{6}^{2}}-\left( 4\times \left( -3 \right)\times \left( -2 \right) \right)}}{2\times \left( -3 \right)} \\ & =\frac{-6\pm 3.464}{-6} \\ & =\frac{-6+3.464}{-6}\ \ \text{or}\ \ \frac{-6-3.464}{-6} \\ & =0.422\ \ \text{or}\ \ 1.577 \end{align}$ This shows that the x intercept occurs at the coordinates, $\left( 1.577,0 \right)$ and $\left( 0.422,0 \right)$.
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