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: 43

Answer

$x^2+\frac{2x^2+7x+5}{(x^2+1)(x-2)}=x^2+\frac{-x-1}{x^2+1}+\frac{3}{x-2}$

Work Step by Step

$\frac{x^5-2x^4+x^3+x+5}{x^3-2x^2+x-2}$, since the degree of the numerator is larger than the degree of the denominator: $\begin{array}{lllllll} & & x^{2} & \\ & -- & -- & -- & -- & -- & \\ x^3-2x^2+x-2\ ) & x^5&-2x^{4} & +x^{3} & +x & +5 & \\ & -x^5 & +2x^4 & -x^{3} & +2x^{2} & & & & \\ & -- & -- & & & & \\ & & 2x^{2} & +x+5 & & & \\ \end{array}$ thus, $x^2+\frac{2x^2+7x+5}{x^3-2x^2+x-2}$, factorising the denominator, $x^3-2x^2+x-2=x^2(x-2)+1(x-2)=(x^2+1)(x-2)$, $x^2+\frac{2x^2+7x+5}{(x^2+1)(x-2)}=\frac{Ax+B}{x^2+1}+\frac{C}{x-2}$, $(Ax+B)(x-2)+C(x^2+1)$, $Ax^2-2Ax+Bx-2B+Cx^2+C$, $(A+C)x^2+(-2A+B)x+(-2B+C)=2x^2+x+5$, $\begin{cases} A+C=2\\ -2A+B=1\\ -2B+C=5 \end{cases}$ Multiplying Equation 1 by 2 and adding it to Equation 2. $\begin{cases} 2A+2C=4\\ -2A+B=1\\ -- -- -- --\\ 0A + B + 2C=5 \end{cases}$ Multiplying the addition result of Equation 1&2 by 2 and adding it to Equation 3. $\begin{cases} 2B+4C=10\\ -2B+C=5\\ -- -- -- --\\ 0B + 5C=15 \end{cases}$ thus, $C=3$, substituting back into the equation, $A+3=2, A=-1$. substituting back into the equation $-2B+3=5, B=-1$ Therefore, $x^2+\frac{2x^2+7x+5}{(x^2+1)(x-2)}=x^2+\frac{-x-1}{x^2+1}+\frac{3}{x-2}$
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