Intermediate Algebra (6th Edition)

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

Chapter 8 - Section 8.1 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 485: 55

Answer

$x=\left\{ -1,\dfrac{5}{2} \right\}$

Work Step by Step

Using the completing the square method, the solutions of the given quadratic equation, $ 2x^2-3x-5=0 ,$ is \begin{array}{l}\require{cancel} \dfrac{1}{2}\cdot(2x^2-3x-5)=(0)\cdot\dfrac{1}{2} \\\\ x^2-\dfrac{3}{2}x-\dfrac{5}{2}=0 \\\\ x^2-\dfrac{3}{2}x=\dfrac{5}{2} \\\\ x^2-\dfrac{3}{2}x+\left( -\dfrac{3}{2\cdot2}\right)^2=\dfrac{5}{2}+\left( -\dfrac{3}{2\cdot2}\right)^2 \\\\ x^2-\dfrac{3}{2}x+\dfrac{9}{16}=\dfrac{5}{2}+\dfrac{9}{16} \\\\ \left( x-\dfrac{3}{4} \right)^2=\dfrac{40}{16}+\dfrac{9}{16} \\\\ \left( x-\dfrac{3}{4} \right)^2=\dfrac{49}{16} \\\\ x-\dfrac{3}{4}=\pm\sqrt{\dfrac{49}{16}} \\\\ x-\dfrac{3}{4}=\pm\dfrac{7}{4} \\\\ x=\dfrac{3}{4}\pm\dfrac{7}{4} \\\\ x=\dfrac{3}{4}-\dfrac{7}{4} \\\\ x=-\dfrac{4}{4} \\\\ x=-1 ,\\\\\text{OR}\\\\ x=\dfrac{3}{4}+\dfrac{7}{4} \\\\ x=\dfrac{10}{4} \\\\ x=\dfrac{5}{2} .\end{array} Hence, $ x=\left\{ -1,\dfrac{5}{2} \right\} .$
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