Intermediate Algebra (6th Edition)

Published by Pearson
ISBN 10: 0321785045
ISBN 13: 978-0-32178-504-6

Chapter 8 - Section 8.2 - Solving Quadratic Equations by the Quadratic Formula - Exercise Set - Page 492: 25

Answer

$\left\{ -2-\sqrt{11},-2+\sqrt{11} \right\}$

Work Step by Step

The standard form of the given equation, $ (x+5)(x-1)=2 ,$ is \begin{array}{l}\require{cancel} x(x)+x(-1)+5(x)+5(-1)=2 \\\\ x^2-x+5x-5=2 \\\\ x^2+(-x+5x)+(-5-2)=0 \\\\ x^2+4x-7=0 .\end{array} Using $\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}$ (or the Quadratic Formula), the solutions of the quadratic equation, $ x^2+4x-7=0 ,$ are \begin{array}{l}\require{cancel} \dfrac{-(4)\pm\sqrt{(4)^2-4(1)(-7)}}{2(1)} \\\\= \dfrac{-4\pm\sqrt{16+28}}{2} \\\\= \dfrac{-4\pm\sqrt{44}}{2} \\\\= \dfrac{-4\pm\sqrt{4\cdot11}}{2} \\\\= \dfrac{-4\pm\sqrt{(2)^2\cdot11}}{2} \\\\= \dfrac{-4\pm2\sqrt{11}}{2} \\\\= \dfrac{2(-2\pm\sqrt{11})}{2} \\\\= \dfrac{\cancel{2}(-2\pm\sqrt{11})}{\cancel{2}} \\\\= -2\pm\sqrt{11} .\end{array} Hence, the solutions are $ \left\{ -2-\sqrt{11},-2+\sqrt{11} \right\} .$
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