College Algebra 7th Edition

Published by Brooks Cole
ISBN 10: 1305115546
ISBN 13: 978-1-30511-554-5

Chapter 5, Systems of Equations and Inequalities - Section 5.3 - Partial Fractions - 5.3 Exercises - Page 462: 28

Answer

$\frac{3x^2+5x-13}{(3x+2)(x-2)^2}=\frac{-135}{192x+128}+\frac{109}{64x-128}+\frac{9}{8(x-2)^2}$,

Work Step by Step

$\frac{3x^2+5x-13}{(3x+2)(x^2-4x+4)}$, factorising $4x^2-4x+4=(x-2)(x-2)=(x-2)^2$: $\frac{3x^2+5x-13}{(3x+2)(x+2)(x-2)}=\frac{A}{3x+2}+\frac{B}{x-2}+\frac{C}{(x-2)^2}$, $3x^2+5x-13=A(x-2)(x-2)+B(3x+2)(x-2)+C(3x+2)$, $3x^2+5x-13=A(x^2-4x+4)+B(3x^2-4x-4)+C(3x+2)$, $3x^2+5x-13=(A+3B)x^2+(-4A-4B+3C)x+(4A-4B+2C)=3x^2+5x-13$ $\begin{cases} & A & +3B & = 3&\\ & -4A & -4B & +3C= 5&\\ & 4A & -4B & +2C =-13&\\ \end{cases}$ Adding Equation $2$ and Equation $3$, $\begin{cases} & -4A & -4B & +3C =5\\ & 4A & -4B & +2C = -13\\ &-- -- & -- -- & -- -- &\\ & +0A & -8B & +5C = -8 \end{cases}$ Multiplying Equation $1$ by $4$ and Adding it to Equation $2$, $\begin{cases} & 4A & +12B & +0C =12\\ & -4A & -4B & +3C = 5\\ & -- -- & -- -- & -- -- &\\ & 0A & 8B & +3C = 17 \end{cases}$ Adding the result of the first Addition and the result of the second addition: $\begin{cases} & 8B & +3C = 17\\ & -8B & +5C =-8\\ & -- -- & -- --& \\ & 0B & 8C = 9 \end{cases}$ thus, $C=\frac{9}{8}$ Substituting back $C=\frac{9}{8}$ into the equation, $8B+\frac{27}{8}=17, B=\frac{109}{64}$. Substituting $B$ into the first Equation, $A+\frac{327}{64}=, A=\frac{-135}{64}$. Therefore, $\frac{3x^2+5x-13}{(3x+2)(x-2)^2}=\frac{-135}{192x+128}+\frac{109}{64x-128}+\frac{9}{8(x-2)^2}$,
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