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: 39

Answer

$x=-1-i\sqrt{2} \text{ OR } x=-1+i\sqrt{2} $

Work Step by Step

In the given equation, \begin{align*} x^2+2x+3=0 ,\end{align*} $a= 1 ,$ $b= 2 ,$ and $c= 3 .$ Using the Quadratic Formula which is given by $x=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a},$ then \begin{align*}\require{cancel}x&= \dfrac{-2\pm\sqrt{2^2-4(1)(3)}}{2(1)} \\\\&= \dfrac{-2\pm\sqrt{4-12}}{2} \\\\&= \dfrac{-2\pm\sqrt{-8}}{2} \\\\&= \dfrac{-2\pm\sqrt{-1}\cdot\sqrt{4}\cdot\sqrt{2}}{2} \\\\&= \dfrac{-2\pm\sqrt{-1}\cdot2\cdot\sqrt{2}}{2} \\\\&= \dfrac{-2\pm i\cdot2\cdot\sqrt{2}}{2} &\text{ (use $i=\sqrt{-1}$)} \\\\&= \dfrac{-2\pm 2i\sqrt{2}}{2} \\\\&= \dfrac{-\cancel2^1\pm \cancel2^1i\sqrt{2}}{\cancel2^1} &\text{ (divide by $2$)} \\\\&= -1\pm i\sqrt{2} .\end{align*} The solutions are $ x=-1-i\sqrt{2} \text{ and } x=-1+i\sqrt{2} .$
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