Precalculus (6th Edition) Blitzer

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

Chapter 2 - Review Exercises - Page 429: 12

Answer

The solution set for the quadratic equation, $2{{x}^{2}}-6x+5=0$ is $\left\{ \frac{3}{2}\pm \frac{1}{2}i \right\}$.

Work Step by Step

Consider quadratic equation, $2{{x}^{2}}-6x+5=0$ Compare the equation with the standard quadratic equation $a{{x}^{2}}+bx+c=0\text{ , }\left( a\ne 0 \right)$. Here, $a=2,\text{ }b=-6\text{ and }c=5$ Apply the quadratic formula $x=\frac{-b\pm \sqrt{{{b}^{2}}-4ac}}{2a}$ Substitute 2 for a, $-6$ for b and 5 for c. $x=\frac{-\left( -6 \right)\pm \sqrt{{{\left( -6 \right)}^{2}}-4\left( 2 \right)\left( 5 \right)}}{2\left( 2 \right)}$ Simplify the radical. $\begin{align} & x=\frac{-\left( -6 \right)\pm \sqrt{{{\left( -6 \right)}^{2}}-4\left( 2 \right)\left( 5 \right)}}{2\left( 2 \right)} \\ & =\frac{6\pm \sqrt{36-40}}{4} \\ & =\frac{6\pm \sqrt{-4}}{4} \end{align}$ As $i=\sqrt{-1}$ Therefore, $\begin{align} & x=\frac{6\pm \sqrt{-1}\sqrt{4}}{4} \\ & =\frac{6\pm 2i}{4} \\ & =\frac{2\left( 3\pm i \right)}{4} \\ & =\frac{3\pm i}{2} \end{align}$ Convert it to standard form. $\begin{align} & x=\frac{3\pm i}{2} \\ & =\frac{3}{2}\pm \frac{1}{2}i \end{align}$ The solutions of the quadratic are complex conjugates of each other. Hence, the solution set for the quadratic equation $2{{x}^{2}}-6x+5=0$ is $\left\{ \frac{3}{2}\pm \frac{1}{2}i \right\}$.
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