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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 : 121 of 271
Marks: +1, -0
5x(x+1)(x2−4)\frac{5x}{(x+1)(x^2-4)}
Solution:  
Let I=∫5x(x+1)(x2−4)dxI=\int\frac{5x}{(x+1)(x^2-4)}dx
Let 5x(x+1)(x2−4)\frac{5x}{(x+1)(x^2-4)} =5x(x+1)(x+2)(x−2)=\frac{5x}{(x+1)(x+2)(x-2)} =Ax+1+Bx+2+Cx−2=\frac{A}{x+1}+\frac{B}{x+2}+\frac{C}{x-2}
⇒ 5x = A(x + 2) (x – 2) + B(x + 1) (x – 2) + C (x + 1) (x + 2) ...(i)
Putting x = –1 in (i), we get – 5 = A(–1 + 2) (–1 –2) ⇒ A =53=\frac{5}{3}
Putting x = –2 in (i), we get – 10 = (–2 + 1)(–2 – 2) ⇒ B =−52=-\frac{5}{2}
Putting x = 2 in (i), we get 10 = C(2 + 1) (2 + 2) ⇒ C =56=\frac{5}{6}
∴5x(x+1)(x2−4)\therefore \frac{5x}{(x+1)(x^2-4)} =53(x+1)−52(x+2)+56(x−2)=\frac{5}{3(x+1)}-\frac{5}{2(x+2)}+\frac{5}{6(x-2)}
∴I=∫5x(x+1)(x2−4)dx\therefore I=\int\frac{5x}{(x+1)(x^2-4)}dx =53∫dxx+1−52∫dxx+2+56∫dxx−2=\frac{5}{3}\int\frac{dx}{x+1}-\frac{5}{2}\int\frac{dx}{x+2}+\frac{5}{6}\int\frac{dx}{x-2}
=53log⁡∣x+1∣−52log⁡∣x+2∣+56log⁡∣x−2∣+C=\frac{5}{3}\log|x+1|-\frac{5}{2}\log|x+2|+\frac{5}{6}\log|x-2|+C
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