Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 8 - Techniques of Integration - 8.5 The Method of Partial Fractions - Exercises - Page 423: 19

Answer

$$2 \ln |x-1|-\frac{1}{(x-1)}-2 \ln |x-2|-\frac{1}{(x-2)}+C$$

Work Step by Step

Given $$\int \frac{d x}{(x-1)^{2}(x-2)^{2}}$$ Since \begin{align*} \frac{1}{(x-1)^{2}(x-2)^{2}}&=\frac{A}{(x-1)}+\frac{B}{(x-1)^{2}}+\frac{C}{(x-2)}+\frac{D}{(x-2)^{2}}\\ &= \frac{A(x-1)(x-2)^{2}+B(x-2)^{2}+C(x-1)^{2}(x-2)+D(x-1)^{2}}{(x-1)^{2}(x-2)^{2}}\\ 1&=A(x-1)(x-2)^{2}+B(x-2)^{2}+C(x-1)^{2}(x-2)+D(x-1)^{2} \end{align*} Then \begin{align*} \text{at } x&= 2 \ \ \ \ \to D=1 \\ \text{at } x&= 1\ \ \ \ \to B=1\\ \text{at } x&= 0\ \ \ \ \to 2A+C=2\\ \text{at } x&= -1\ \ \ \ \to 3A+2C=2\\ \end{align*} Hence $A=2,\ \ C=-2$ and \begin{aligned} \int \frac{d x}{(x-1)^{2}(x-2)^{2}} &=\int \frac{2 d x}{(x-1)}+\int \frac{d x}{(x-1)^{2}}-\int \frac{2 d x}{(x-2)}+\int \frac{d x}{(x-2)^{2}} \\ &=2 \int \frac{d x}{(x-1)}+\int(x-1)^{-2} d x-2 \int \frac{d x}{(x-2)}+\int(x-2)^{-2} d x\\&=2 \ln |x-1|-\frac{1}{(x-1)}-2 \ln |x-2|-\frac{1}{(x-2)}+C \end{aligned}
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