College Algebra (6th Edition)

Published by Pearson
ISBN 10: 0-32178-228-3
ISBN 13: 978-0-32178-228-1

Chapter 1 - Mid-Chapter Check Point - Page 165: 12

Answer

$$x= 4$$

Work Step by Step

We have $$\frac{2x}{x^2+6x+8} = \frac{x}{x+4} - \frac{2}{x+2}$$ As we see we have a rational expression so we need to multiply each side of the equation by the minimum common multiple of the denominators. Note that $(x+4)(x+2) = x^2 + 6x + 8$ so the minimun common multiple of the denominators is $(x+4)(x+2)$. Multiplying each side of the equation by mcm $$(x+4)(x+2)(\frac{2x}{x^2+6x+8}) = (x+4)(x+2)(\frac{x}{x+4} - \frac{2}{x+2})$$ $$\frac{(x+4)(x+2)(2x)}{x^2+6x+8} = \frac{(x+4)(x+2)(x)}{x+4} - \frac{(x+4)(x+2)(2)}{x+2}$$ Simplifying each rational expression $$2x = (x+2)(x) - (x+4)(2)$$ Doing all the multiplications in order to eliminate the parenthesis $$2x = (x)(x) + (2)(x) - (x)(2) - (4)(2)$$ $$2x = x^2 + 2x -2x - 8$$ Taking all the terms to the left side of the equation and equalizing to $0$ $$2x - x^2 - 2x + 2x + 8 =0$$ Simplifying $$-x^2 +2x +8 = 0$$ Multiplying each side by $-1$ $$x^2 -2x -8 = 0$$ Note we can factorize the expression $$(x-4)(x+2) = 0$$ Equalizing each parenthesis to $0$ we can get our two values. For the first one $x-4 = 0$ so $x_{1}= 4$ For the second one $x+2 = 0$ so $x_{2} = -2$ Substituting each one of the value $x = 4$ results to be a solution but $x=-2$ not. So the only solution for this equation is $x = 4$.
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