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: 51

Answer

the solution set is\[\left\{ -\frac{1}{3},-\frac{7}{2} \right\}\].

Work Step by Step

Step 1: Shift all nonzero terms to left side and obtain zero on the other side. Consider the expression\[x\left( 6x+23 \right)+7=0\]. Apply the distributive law to get, \[6{{x}^{2}}+23x+7=0\] Step 2: Find the factor of the above equation: Consider the equation \[6{{x}^{2}}+23x+7=0\]. Factorize it as follows: \[\begin{align} & 6{{x}^{2}}+23x+7=0 \\ & 6{{x}^{2}}+21x+2x+7=0 \\ & 3x\left( 2x+7 \right)+1\left( 2x+7 \right)=0 \\ & \left( 2x+7 \right)\left( 3x+1 \right)=0 \end{align}\] Steps 3 and 4: Set each factor equal to zero and solve the resulting equation: From step 2, \[\left( 2x+7 \right)\left( 3x+1 \right)=0\]. By the zero product principal, either \[\left( 2x+7 \right)=0\]or\[\left( 3x+1 \right)=0\]. Now \[\left( 2x+7 \right)=0\]implies that \[x=-\frac{7}{2}\]and \[\left( 3x+1 \right)=0\] implies that\[x=-\frac{1}{3}\]. Step 5: Check the solution in the original equation. Check for\[x=-\frac{7}{2}\]. So consider, \[\begin{align} & 6{{x}^{2}}+23x+7=0 \\ & 6{{\left( -\frac{7}{2} \right)}^{2}}+23\left( -\frac{7}{2} \right)+7=0 \\ & \frac{147}{2}-\frac{161}{2}+7=0 \\ & 0=0 \end{align}\] Now check for\[x=-\frac{1}{3}\]. So consider, \[\begin{align} & 6{{x}^{2}}+23x+7=0 \\ & 6{{\left( -\frac{1}{3} \right)}^{2}}+23\left( -\frac{1}{3} \right)+7=0 \\ & \frac{2}{3}-\frac{23}{3}+7=0 \\ & 0=0 \end{align}\] Hence, the solution set is\[\left\{ -\frac{1}{3},-\frac{7}{2} \right\}\].
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