Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Appendix A - Review - A.5 Rational Expressions - A.5 Assess Your Understanding - Page A42: 35

Answer

$-\dfrac{2x(x^2-2)}{(x+2)(x^2-x-3)}$

Work Step by Step

Simplify the numerator $\frac{x-2}{x+2}+\frac{x-1}{x+1}$. The LCD is $(x+2)(x+1)$. Make the expresions simillar by multiplying $x+1$ to both the numerator and the denominator of the first expression and $x+2$ to the second expression to obtain: $=\dfrac{(x-2)(x+1)}{(x+2)(x+1)}+\dfrac{(x-1)(x+2)}{(x+1)(x+2)}$ $=\dfrac{(x-2)(x+1)+(x-1)(x+2)}{(x+2)(x+1)}$ Use FOIL method. $=\dfrac{x^2+x-2x-2+x^2+2x-x-2}{(x+2)(x+1)}$ Simplify. $=\dfrac{2x^2-4}{(x+2)(x+1)}$ Factor. $=\dfrac{2(x^2-2)}{(x+2)(x+1)}$ Simplify the denominator $\frac{x}{x+1}-\frac{2x-3}{x}$ The LCD is $x(x+1)$. Make the expressions similar by multiplying $x$ to both the numerator and the denominator of the first expression and $x+1$ to the second expression to obtain: $=\dfrac{x^2}{x(x+1)}-\dfrac{(2x-3)(x+1)}{x(x+1)}$ $=\dfrac{x^2-(2x-3)(x+1)}{x(x+1)}$ Use FOIL method. $=\dfrac{x^2-(2x^2+2x-3x-3)}{x(x+1)}$ $=\dfrac{x^2-2x^2-2x+3x+3}{x(x+1)}$ $=\dfrac{-x^2+x+3}{x(x+1)}$ Factor. $=\dfrac{-(x^2-x-3)}{x(x+1)}$ Substitute back into the given expression. $=\dfrac{\dfrac{2(x^2-2)}{(x+2)(x+1)}}{\dfrac{-(x^2-x-3)}{x(x+1)}}$ Use the rule $\frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \cdot \frac{d}{c}$ to obtain: . $=\dfrac{2(x^2-2)}{(x+2)(x+1)}\cdot \dfrac{x(x+1)}{-(x^2-x-3)}$ Cancel common factors: $=-\dfrac{2x(x^2-2)}{(x+2)(x^2-x-3)}$ Hence, the lowest term is: $-\dfrac{2x(x^2-2)}{(x+2)(x^2-x-3)}$
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