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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 : 113 of 271
Marks: +1, -0
3x−1(x−1)(x−2)(x−3)\frac{3x-1}{(x-1)(x-2)(x-3)}
Solution:  
Let I=∫3x−1(x−1)(x−2)(x−3)dxI=\int \frac{3x-1}{(x-1)(x-2)(x-3)}dx
Let 3x−1(x−1)(x−2)(x−3)\frac{3x-1}{(x-1)(x-2)(x-3)} =Ax−1+Bx−2+Cx−3=\frac{A}{x-1}+\frac{B}{x-2}+\frac{C}{x-3}
⇒3x−1=A(x−2)(x−3)+B(x−1)(x−3)+C(x−1)(x−2)\Rightarrow 3x-1 = A(x-2)(x-3)+B(x-1)(x-3)+C(x-1)(x-2)...(i)
Putting x=1x=1 in (i), we get
3 - 1 = A(1 - 2) (1- 3) ⇒ 2 = A (-1) (-2) ⇒ A = 1
Putting x = 2 in (i), we get
6 – 1 = B(2 – 1) (2 – 3) ⇒ 5 = B(1) (–1) ⇒ B = –5
Putting x = 3 in (i), we get
9 – 1 = C(3 – 1) (3 – 2) ⇒ 8 = C(2) (1) ⇒ C = 4
∴3x−1(x−1)(x−2)(x−3)\therefore \frac{3x-1}{(x-1)(x-2)(x-3)} =1x−1−5x−2+4x−3=\frac{1}{x-1}-\frac{5}{x-2}+\frac{4}{x-3}
∴∫3x−1(x−1)(x−2)(x−3)\therefore \int \frac{3x-1}{(x-1)(x-2)(x-3)} =∫1x−1dx−5∫1x−2dx+4∫1x−3dx=\int \frac{1}{x-1}dx -5\int \frac{1}{x-2}dx +4\int \frac{1}{x-3}dx
=log⁡∣x−1∣−5log⁡∣x−2∣+4log⁡∣x−3∣+C=\log|x-1| -5\log|x-2| +4\log|x-3| + C
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