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: 39

Answer

$x=-\dfrac{1}{2}\pm\dfrac{\sqrt{5}}{2}$

Work Step by Step

Using the completing the square method, then, \begin{array}{l} x^2+x-1=0\\ x^2+x=1\\ x^2+x+\left( \dfrac{1}{2} \right)^2=1+\left( \dfrac{1}{2}\right)^2\\ x^2+x+\dfrac{1}{4}=1+\dfrac{1}{4}\\ \left( x+\dfrac{1}{2} \right)^2=\dfrac{5}{4}\\ x+\dfrac{1}{2}=\pm\sqrt{\dfrac{5}{4}}\\ x=-\dfrac{1}{2}\pm\dfrac{\sqrt{5}}{2} .\end{array}
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