Intermediate Algebra: Connecting Concepts through Application

Published by Brooks Cole
ISBN 10: 0-53449-636-9
ISBN 13: 978-0-53449-636-4

Chapter 8 - Radical Functions - 8.4 Solving Radical Equations - 8.4 Exercises - Page 654: 46

Answer

$x=183+ 8\sqrt{ 517}\approx 364.90 $

Work Step by Step

Given $$\sqrt{6x-5}=4+\sqrt{5x+2}.$$ First we square both sides to eliminate one of the radicals: $$\begin{aligned} (\sqrt{6x-5})^2&=(4+\sqrt{5x+2})^2\\ 6x-5&=16+8\sqrt{5x+2}+5x+2\\ x-23&=8\sqrt{5x+2}. \end{aligned}$$ We square both sides again to eliminate the other radical: $$\begin{aligned} (x-23)^2&=(8\sqrt{5x+2})^2\\ x^2-46x+529&=64(5x+2)\\ x^2-46x+529&=320x+128\\ x^2-366x+401&=0. \end{aligned}$$ Solve the equation: $$\begin{aligned} x&=\frac{-(-366)\pm\sqrt{(-366)^2-4(1)(401)}}{2(1)}\\ &=\frac{366\pm 16\sqrt{517}}{2}\\ &=183\pm8\sqrt{517}. \end{aligned}$$ The solutions are: $$ \begin{aligned} x&=183-8\sqrt{517}\\ x&=183+8\sqrt{517}. \end{aligned}$$ Check: $$ \begin{aligned} \sqrt{6(183-8\sqrt{517})-5}&\stackrel{?}{=}4+\sqrt{5(183-8\sqrt{517})+2}\\ \sqrt{1093-48\sqrt{517}}&\stackrel{?}{=}4+\sqrt{917-40\sqrt{517}}\\ 24-\sqrt{517}&\stackrel{?}{=}4+\sqrt{517}-20\\ 1.26&\not=6.74\\\\ \sqrt{6(183+8\sqrt{517})-5}&\stackrel{?}{=}4+\sqrt{5(183+8\sqrt{517})+2}\\ \sqrt{1093+48\sqrt{517}}&\stackrel{?}{=}4+\sqrt{917+40\sqrt{517}}\\ 24+\sqrt{517}&\stackrel{?}{=}4+\sqrt{517}+20\\ 24+\sqrt{517}&=24+\sqrt{517}\checkmark. \end{aligned}$$ The only solution is $$x=183+8\sqrt{517}\approx 364.90.$$ The solution is $x=183+ 8\sqrt{ 517}\approx 364.90 $
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