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 399: 35

Answer

\[\left\{ -\frac{5}{4},2 \right\}\]

Work Step by Step

Consider the expression\[\left( 4x+5 \right)\left( x-2 \right)=0\]. Then, by the zero product principal either \[\left( 4x+5 \right)=0\]or\[\left( x-2 \right)=0\]. Now \[\left( 4x+5 \right)=0\]implies that \[x=-\frac{5}{4}\]and \[\left( x-2 \right)=0\] implies that\[x=2\]. Next, check the proposed solution by substituting it in the original equation. Check for\[x=-\frac{5}{4}\]. So consider, \[\begin{align} & \left( 4x+5 \right)\left( x-2 \right)=0 \\ & \left( 4\times \left( -\frac{5}{4} \right)+5 \right)\times \left( -\frac{5}{4}-2 \right)=0 \\ & 0\left( -\frac{5}{4}-2 \right)=0 \\ & 0=0 \end{align}\] Now check for\[x=2\]. So consider, \[\begin{align} & \left( 4x+5 \right)\left( x-2 \right)=0 \\ & \left( 4\times 2+5 \right)\times \left( 2-2 \right)=0 \\ & 13\left( 0 \right)=0 \\ & 0=0 \end{align}\] Hence, the solution set is\[\left\{ -\frac{5}{4},2 \right\}\].
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