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: 29

Answer

$\dfrac{2(2x^2+5x-2)}{(x-2)(x+2)(x+3)}$

Work Step by Step

Factor $x^2+x-6$. With $a=1$ and $c=-24$, $ac=1(-24)=-24$. The factors of $-24$ whose sum is equal to $b=5$ are $3$ and $-1$. Rewrite $x$ as $3x-2x$. $=x^2+3x-2x-6$ Group the terms. $=(x^2+3x)+(-2x-6)$ Factor each group. $=x(x+3)-2(x+3)$ Factor out $(x+3)$. $=(x+3)(x-2)$ Factor $x^2-4$: $=x^2-2^2$ Use special formula $a^2-b^2=(a+b)(a-b)$. $=(x+2)(x-2)$ Substitute back the factored form of each polynomial into the given expression. $=\dfrac{4x}{(x+2)(x-2)}-\dfrac{2}{(x+3)(x-2)}$ The LCD is $(x-2)(x+2)(x+3)$. Make the expressions similar by multiplying $x+3$ to both the numerator and denominator of the first expression, and $x+2$ to the second expression to obtain: $=\dfrac{4x}{(x+2)(x-2)}\cdot \dfrac{x+3}{x+3}-\dfrac{2}{(x+3)(x-2)}\cdot \dfrac{x+2}{x+2}$ $=\dfrac{4x(x+3)}{(x-2)(x+2)(x+3)}-\dfrac{2(x+2)}{(x-2)(x+2)(x+3)}$ Add numerators and retain the denominator. $=\dfrac{4x(x+3)-2(x+2)}{(x-2)(x+2)(x+3)}$ Use the distributive property. $=\dfrac{4x^2+12x-2x-4}{(x-2)(x+2)(x+3)}$ $=\dfrac{4x^2+10x-4}{(x-2)(x+2)(x+3)}$ Factor out $2$ from the numerator. $=\dfrac{2(2x^2+5x-2)}{(x-2)(x+2)(x+3)}$ The numerator can no longer be factored. Hence, the lowest term is: $\dfrac{2(2x^2+5x-2)}{(x-2)(x+2)(x+3)}$
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