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: 78

Answer

the solution set is\[\left\{ 1,\,\,\frac{5}{7} \right\}\].

Work Step by Step

The given equation can be written as\[7x\left( x-2 \right)=3-2\left( x+4 \right)\]. Apply distributive law on both the sides as follows: \[\begin{align} & 7x\left( x-2 \right)=3-2\left( x+4 \right) \\ & 7{{x}^{2}}-14=3-2x-8 \\ & 7{{x}^{2}}-14=-2x-5 \\ \end{align}\] Simplifying \[7{{x}^{2}}-12x+5=0\] Compare the given equation with the equation\[a{{x}^{2}}+bx+c=0\], where\[a=7,\ b=-12,\text{ and }c=5\]. Now, put these values in the quadratic formula \[x=\frac{-b\pm \sqrt{{{b}^{2}}-4ac}}{2a}\] \[\begin{align} & x=\frac{-\left( -12 \right)\pm \sqrt{{{\left( -12 \right)}^{2}}-4\times \left( 7 \right)\times \left( 5 \right)}}{2\times 7} \\ & =\frac{12\pm \sqrt{144-140}}{4} \\ & =\frac{-12\pm \sqrt{4}}{4} \\ & =\frac{-12\pm 2}{4} \end{align}\] This gives,\[x=1,\,\,\frac{5}{7}\] Hence, the solution set is\[\left\{ 1,\,\,\frac{5}{7} \right\}\].
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