Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 6 - Algebra: Equations and Inequalities - 6.5 Quadratic Equations - Exercise Set 6.5 - Page 400: 64

Answer

The solution set is\[\left\{ -\frac{1}{3},\frac{5}{3} \right\}\].

Work Step by Step

The given equation can be written as \[9{{x}^{2}}-12x-5=0\]. Compare the given equation with the equation\[a{{x}^{2}}+bx+c=0\]. Here,\[a=9,\,\,b=-12,\text{ and }c=-5\]. Now put these values in the quadratic formula: \[x=\frac{-b\pm \sqrt{{{b}^{2}}-4ac}}{2a}\] That is, \[\begin{align} & x=\frac{12\pm \sqrt{{{\left( -12 \right)}^{2}}-4\times 9\times \left( -5 \right)}}{2\times 9} \\ & =\frac{12\pm \sqrt{144+180}}{18} \\ & =\frac{12\pm \sqrt{324}}{18} \\ & =\frac{12\pm 18}{18} \end{align}\] Further simplify it to get, \[\begin{align} & x=\frac{12\pm 18}{18} \\ & =\frac{30}{18},-\frac{6}{18} \\ & =\frac{5}{3},-\frac{1}{3} \end{align}\] Hence, the solution set is\[\left\{ -\frac{1}{3},\frac{5}{3} \right\}\].
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