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: 50

Answer

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

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: \[3{{x}^{2}}-4x-15=0\] Step 2: Find the factor of the above equation: Consider the equation, \[3{{x}^{2}}-4x-15=0\]. Factorize it as follows: \[\begin{align} & 3{{x}^{2}}-4x-15=0 \\ & 3{{x}^{2}}-9x+5x-15=0 \\ & 3x\left( x-3 \right)+5\left( x-3 \right)=0 \\ & \left( 3x+5 \right)\left( x-3 \right)=0 \end{align}\] Steps 3 and 4: Set each factor equal to zero and solve the resulting equation: From step 2, \[\left( 3x+5 \right)\left( x-3 \right)=0\] By the zero product principal, either \[\left( 3x+5 \right)=0\]or\[\left( x-3 \right)=0\]. Now \[\left( 3x+5 \right)=0\]implies that \[x=-\frac{5}{3}\]and \[\left( x-3 \right)=0\] implies that\[x=3\]. Step 5: Check the solution in the original equation: Check for\[x=3\]. So consider, \[\begin{align} & 3{{x}^{2}}-4x-15=0 \\ & 3{{\left( 3 \right)}^{2}}-4\left( 3 \right)-15=0 \\ & 27-12-15=0 \\ & 0=0 \end{align}\] Now check for\[x=-\frac{5}{3}\]. So consider, \[\begin{align} & 3{{x}^{2}}-4x-15=0 \\ & 3{{\left( -\frac{5}{3} \right)}^{2}}-4\left( -\frac{5}{3} \right)-15=0 \\ & \frac{25}{3}+\frac{20}{3}-15=0 \\ & 0=0 \end{align}\] Hence, the solution set is\[\left\{ -\frac{5}{3},3 \right\}\].
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