Intermediate Algebra (12th Edition)

Published by Pearson
ISBN 10: 0321969359
ISBN 13: 978-0-32196-935-4

Chapter 8 - Section 8.3 - Equations Quadratic in Form - 8.3 Exercises - Page 530: 67

Answer

$\left\{-\dfrac{1}{3},\dfrac{1}{6}\right\}$

Work Step by Step

Let $z= \dfrac{1}{3x-1} $. Then the given equation, $ 2+\dfrac{5}{3x-1}=\dfrac{-2}{(3x-1)^2} ,$ is equivalent to \begin{align*} 2+5\cdot\dfrac{1}{3x-1}&=-2\cdot\dfrac{1}{(3x-1)^2} \\\\ 2+5z&=-2z^2 \\ 2z^2+5z+2&=0 .\end{align*} Using factoring of trinomials, the equation above is equivalent to \begin{align*} (z+2)(2z+1)&=0 .\end{align*} Equating each factor to zero (Zero Product Property) and solving for the variable, then \begin{array}{l|r} z+2=0 & 2z+1=0 \\ z=-2 & 2z=-1 \\\\ & z=-\dfrac{1}{2} .\end{array} Since $z= \dfrac{1}{3x-1} ,$ by back substitution, then \begin{array}{l|r} \dfrac{1}{3x-1}=-2 & \dfrac{1}{3x-1}=-\dfrac{1}{2} .\end{array} By cross-multiplication and the properties of equality, the equations above are equivalent to \begin{array}{l|r} 1=-2(3x-1) & 1(2)=(3x-1)(-1) \\ 1=-6x+2 & 2=-3x+1 \\ 6x=2-1 & 3x=1-2 \\ 6x=1 & 3x=-1 \\\\ x=\dfrac{1}{6} & x=-\dfrac{1}{3} .\end{array} Checking the solutions by substitution in the given equation results to \begin{array}{l|r} \text{If }x=\dfrac{1}{6}: & \text{If }x=-\dfrac{1}{3} \\\\ 2+\dfrac{5}{3\left(\frac{1}{6}\right)-1}\overset{?}=\dfrac{-2}{\left(3\left(\frac{1}{6}\right)-1\right)^2} & 2+\dfrac{5}{3\left(-\frac{1}{3}\right)-1}\overset{?}=\dfrac{-2}{\left(3\left(-\frac{1}{3}\right)-1\right)^2} \\\\ 2+\dfrac{5}{\frac{1}{2}-1}\overset{?}=\dfrac{-2}{\left(\frac{1}{2}-1\right)^2} & 2+\dfrac{5}{-1-1}\overset{?}=\dfrac{-2}{\left(-1-1\right)^2} \\\\ 2+\dfrac{5}{-\frac{1}{2}}\overset{?}=\dfrac{-2}{\left(-\frac{1}{2}\right)^2} & 2+\dfrac{5}{-2}\overset{?}=\dfrac{-2}{\left(-2\right)^2} \\\\ 2-10\overset{?}=\dfrac{-2}{\frac{1}{4}} & \dfrac{4}{2}-\dfrac{5}{2}\overset{?}=\dfrac{-2}{4} \\\\ -8\overset{\checkmark}=-8 & -\dfrac{1}{2}\overset{\checkmark}=-\dfrac{1}{2} .\end{array} Since all solutions satisfy the original equation, then the solution set of the equation $ 2+\dfrac{5}{3x-1}=\dfrac{-2}{(3x-1)^2} $ is $\left\{-\dfrac{1}{3},\dfrac{1}{6}\right\}$.
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