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NCERT Class XII Mathematics Chapter - - Solutions

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Exercise - 7.5
Integrate the rational functions in Exercises 111 to 131.
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Question : 118 of 271
Marks: +1, -0
x(x−1)2(x+2)\frac{x}{(x-1)^2(x+2)}
Solution:  
Let x(x−1)2(x+2)\frac{x}{(x-1)^2(x+2)} =Ax−1+B(x−1)2+Cx+2= \frac{A}{x-1} + \frac{B}{(x-1)^2} + \frac{C}{x+2}
⇒ x = A(x – 1)(x + 2) + B(x + 2) + C(x – 1)2 ...(i)
Comparing coefficient of x2x^2 on both sides of (i), we get, 0 = A + C
Putting x = –2 in (i), we get −2=C(−2−1)2-2 = C(-2-1)^2 ⇒C=−29\Rightarrow C = -\frac{2}{9} ⇒A=−C+29\Rightarrow A = -C + \frac{2}{9}
Putting x = 1 in (i), we get 1 = B(1 + 2) ⇒ B =13= \frac{1}{3}
∴∫x(x−1)2(x+2)dx=∫29(x−1)dx+∫13(x−1)2dx−∫29(x+2)dx\therefore \int \frac{x}{(x-1)^2(x+2)} dx = \int \frac{2}{9(x-1)} dx + \int \frac{1}{3(x-1)^2} dx - \int \frac{2}{9(x+2)} dx
=29log⁡∣x−1∣+13×(x−1)−1−1−29log⁡∣x+2∣+C= \frac{2}{9} \log |x-1| + \frac{1}{3} \times \frac{(x-1)^{-1}}{-1} - \frac{2}{9} \log |x+2| + C
=29log⁡∣x−1x+2∣−13(x−1)+C= \frac{2}{9} \log \left| \frac{x-1}{x+2} \right| - \frac{1}{3(x-1)} + C
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