College Algebra (6th Edition)

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

Chapter 5 - Systems of Equations and Inequalities - Exercise Set 5.3 - Page 550: 16

Answer

$ \displaystyle \frac{1}{4(x-1)}+\frac{3}{4(x+3)}$

Work Step by Step

First, factor the trinomial in the denominator (Two factors of $-3$ that add to $+2$ are $3$ and $-1$) $2x^{2}-5x-3=(x-1)(x+3)$ (see p.541: Include one partial fraction with a $constant$ numerator for each distinct linear factor in the denominator.) $\displaystyle \frac{x}{(x-1)(x+3)}=\frac{A}{(x-1)}+\frac{B}{(x+3)}$ multiply both sides with $(x-1)(x+3)\quad $(LCD) $x=A(x+3)+B(x-1)$ $ x=Ax+3A+Bx-B\qquad$ /group like terms... $x+0=x(A+B)+(3A-B)$ ... we now equate the coefficients of like powers... $\left\{\begin{array}{ll} I. & 1=A+B\\ II. & 0=3A-B \end{array}\right.\qquad $solve the system $(II+I)$ eliminates $B...$ $1+0=3A+A-B+B$ $1=4A$ $A=\displaystyle \frac{1}{4}$ back substitute: $1=A+B$ $1=\displaystyle \frac{1}{4}+B$ $B=\displaystyle \frac{3}{4}$ Rewrite the setup decomposition with $A=\displaystyle \frac{1}{4}, B=\frac{3}{4}$ $\displaystyle \frac{x}{(x-1)(x+3)}=\frac{\frac{1}{4}}{(x-1)}+\frac{\frac{3}{4}}{(x+3)}$ $\displaystyle \frac{x}{(x-1)(x+3)}= \frac{1}{4(x-1)}+\frac{3}{4(x+3)}$
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