Algebra 2 Common Core

Published by Prentice Hall
ISBN 10: 0133186024
ISBN 13: 978-0-13318-602-4

Chapter 4 - Quadratic Functions and Equations - 4-8 Complex Numbers - Practice and Problem-Solving Exercises - Page 253: 44

Answer

$x=\dfrac{3-i}{2} \text{ OR } x=\dfrac{3+i}{2}$

Work Step by Step

The given equation, $ 2x(x-3)=-5 ,$ is equivalent to \begin{align*} 2x^2-6x&=-5 &\text{ (use Distributive Property)} \\ 2x^2-6x+5&=0 .\end{align*} Using $ax^2+bx+c=0,$ the equation above has $a= 2 ,$ $b= -6 ,$ and $c= 5 .$ Using the Quadratic Formula which is given by $x=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a},$ then \begin{align*}\require{cancel}x&= \dfrac{-(-6)\pm\sqrt{(-6)^2-4(2)(5)}}{2(2)} \\\\&= \dfrac{6\pm\sqrt{36-40}}{4} \\\\&= \dfrac{6\pm\sqrt{-4}}{4} \\\\&= \dfrac{6\pm\sqrt{-1}\cdot\sqrt{4}}{4} \\\\&= \dfrac{6\pm\sqrt{-1}\cdot2}{4} \\\\&= \dfrac{6\pm i\cdot2}{4} &\text{ (use $i=\sqrt{-1}$)} \\\\&= \dfrac{6\pm 2i}{4} \\\\&= \dfrac{\cancel6^3\pm \cancel2^1i}{\cancel4^2} &\text{ (divide by $2$)} \\\\&= \dfrac{3\pm i}{2} .\end{align*} The solutions are $ x=\dfrac{3-i}{2} \text{ and } x=\dfrac{3+i}{2} .$
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