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: 49

Answer

the solution set is\[\left\{ -2,\frac{9}{5} \right\}\].

Work Step by Step

Step 1: Shift all nonzero terms to left side and obtain zero on the other side. After shifting all nonzero terms to the left side, the above equation becomes: \[5{{x}^{2}}+x-18=0\] Step 2: Find the factor of the above equation: Consider the equation \[5{{x}^{2}}+x-18=0\]. Factorize it as follows: \[\begin{align} & 5{{x}^{2}}+x-18=0 \\ & 5{{x}^{2}}+10x-9x-18=0 \\ & 5x\left( x+2 \right)-9\left( x+2 \right)=0 \\ & \left( 5x-9 \right)\left( x+2 \right)=0 \end{align}\] Steps 3 and 4: Set each factor equal to zero and solve the resulting equation: From step 2, \[\left( 5x-9 \right)\left( x+2 \right)=0\]. By the zero product principal, either \[\left( 5x-9 \right)=0\]or\[\left( x+2 \right)=0\]. Now \[\left( 5x-9 \right)=0\]implies that \[x=\frac{9}{5}\]and \[\left( x+2 \right)=0\] implies that\[x=-2\]. Step 5: Check the solution in the original equation. Check for\[x=-2\]. So consider, \[\begin{align} & 5{{x}^{2}}+x-18=0 \\ & 5{{\left( -2 \right)}^{2}}+1\left( -2 \right)-18=0 \\ & 20-2-18=0 \\ & 0=0 \end{align}\] Now check for\[x=\frac{9}{5}\]. So consider, \[\begin{align} & 5{{x}^{2}}+x-18=0 \\ & 5{{\left( \frac{9}{5} \right)}^{2}}+1\left( \frac{9}{5} \right)-18=0 \\ & \frac{81}{5}+\frac{9}{5}-18=0 \\ & 0=0 \end{align}\] Hence, the solution set is\[\left\{ -2,\frac{9}{5} \right\}\].
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