College Algebra (6th Edition)

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

Chapter 6 - Matrices and Determinants - Cumulative Review Exercises (Chapters 1-6) - Page 658: 15

Answer

$\dfrac{3x^2+17x-38}{(x-3)(x-2)(x+2)}=\dfrac{8}{x-3}-\dfrac{2}{x-2}-\dfrac{3}{x+2}$

Work Step by Step

We are given the fraction: $\dfrac{3x^2+17x-38}{(x-3)(x-2)(x+2)}$ Write the partial fraction decomposition: $\dfrac{3x^2+17x-38}{(x-3)(x-2)(x+2)}=\dfrac{A}{x-3}+\dfrac{B}{x-2}+\dfrac{C}{x+2}$ Multiply all terms by the least common denominator $(x-3)(x-2)(x+2)$: $(x-3)(x-2)(x+2)\cdot\dfrac{3x^2+17x-38}{(x-3)(x-2)(x+2)}=(x-3)(x-2)(x+2)\cdot\dfrac{A}{x-3}+(x-3)(x-2)(x+2)\cdot\dfrac{B}{x-2}+(x-3)(x-2)(x+2)\cdot\dfrac{C}{x+2}$ $3x^2+17x-38=A(x-2)(x+2)+B(x-3)(x+2)+C(x-3)(x-2)$ $3x^2+17x-38=A(x^2-4)+B(x^2-x-6)+C(x^2-5x+6)$ $3x^2+17x-38=Ax^2-4A+Bx^2-Bx-6B+Cx^2-5Cx+6C$ $3x^2+17x-38=(A+B+C)x^2+(-B-5C)x+(-4A-6B+6C)$ Identify the coefficients: $\begin{cases} A+B+C=3\\ -B-5C=17\\ -4A-6B+6C=-38 \end{cases}$ Solve the system: $\begin{cases} 4A+4B+4C=4(3)\\ -B-5C=17\\ -4A-6B+6C=-38 \end{cases}$ $\begin{cases} 4A+4B+4C-4A-6B+6C=12-38\\ -B-5C=17 \end{cases}$ $\begin{cases} -2B+10C=-26\\ -B-5C=17 \end{cases}$ $\begin{cases} -B+5C=-13\\ -B-5C=17 \end{cases}$ $-B+5C-B-5C=-13+17$ $-2B=4$ $B=-2$ $-B-5C=17$ $-(-2)-5C=17$ $5C=-15$ $C=-3$ $A+B+C=3$ $A-2-3=3$ $A-5=3$ $A=8$ The partial fraction decomposition is: $\dfrac{3x^2+17x-38}{(x-3)(x-2)(x+2)}=\dfrac{8}{x-3}-\dfrac{2}{x-2}-\dfrac{3}{x+2}$
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