Precalculus (6th Edition) Blitzer

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

Chapter 2 - Section 2.1 - Complex Numbers - Exercise Set - Page 315: 87

Answer

The solution of the quadratic equation $0=-2{{\left( x-3 \right)}^{2}}+8$ is $\left\{ 1,5 \right\}$.

Work Step by Step

Consider the quadratic equation, $0=-2{{\left( x-3 \right)}^{2}}+8$ Add the term $2{{\left( x-3 \right)}^{2}}$ on both sides, $\begin{align} & 0+2{{\left( x-3 \right)}^{2}}=-2{{\left( x-3 \right)}^{2}}+8+2{{\left( x-3 \right)}^{2}} \\ & 2{{\left( x-3 \right)}^{2}}=8 \end{align}$ Divide both sides by 2, $\begin{align} & 0+2{{\left( x-3 \right)}^{2}}=-2{{\left( x-3 \right)}^{2}}+8+2{{\left( x-3 \right)}^{2}} \\ & \frac{2}{2}{{\left( x-3 \right)}^{2}}=\frac{8}{2} \\ & {{\left( x-3 \right)}^{2}}=4 \end{align}$ Apply the square root property, $\begin{align} & x-3=\pm \sqrt{4} \\ & x-3=\pm 2 \\ & x=3\pm 2 \end{align}$ First take the positive sign, $\begin{align} & x=3+2 \\ & =5 \end{align}$ Secondly, take the negative sign, $\begin{align} & x=3-2 \\ & =1 \end{align}$ Thus, the two values of x are 5 and 1. Thus, the solutions of the quadratic equation $0=-2{{\left( x-3 \right)}^{2}}+8$ are 1 and 5. Check it by substituting the value of x in the equations. Check: For, $x=1$ \[\begin{align} & 0\overset{?}{\mathop{=}}\,-2{{\left( 1-3 \right)}^{2}}+8 \\ & 0\overset{?}{\mathop{=}}\,-2{{\left( -2 \right)}^{2}}+8 \\ & 0\overset{?}{\mathop{=}}\,-8+8 \\ & 0\overset{?}{\mathop{=}}\,0 \end{align}\] Which is true. For, $x=5$ \[\begin{align} & 0\overset{?}{\mathop{=}}\,-2{{\left( 5-3 \right)}^{2}}+8 \\ & 0\overset{?}{\mathop{=}}\,-2{{\left( 2 \right)}^{2}}+8 \\ & 0\overset{?}{\mathop{=}}\,-8+8 \\ & 0\overset{?}{\mathop{=}}\,0 \end{align}\] Which is true. Thus, the solution of the quadratic equation $0=-2{{\left( x-3 \right)}^{2}}+8$ is $\left\{ 1,5 \right\}$.
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