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JEE Main 201322 AprilOnline
Exam
JEE Main
Year
2013
Date
22 April
Mode
Online
Subject
Mathematics
Chapter
Indefinite Integration

JEE Main 2013 · 22 April · Online · Mathematics · Indefinite Integration

If ∫ (x^2-x+1)/(x^2+1) e^ ^ -1 x d x=A(x) e^ ^ -1 x +C , then A(x)...

If ∫x2−x+1x2+1ecot⁡−1xdx=A(x)ecot⁡−1x+C\int \frac{x^2-x+1}{x^2+1} e^{\cot ^{-1} x} d x=A(x) e^{\cot ^{-1} x}+C, then A(x)A(x) is equal to :

Options

  1. A−x-x
  2. Bxx
  3. C1−x\sqrt{1-x}
  4. D1+x\sqrt{1+x}

Correct answer

B. xx

Step-by-step solution

Let I=∫x2−x+1x2+1⋅ecot⁡−1xdx\mathrm{I}=\int \frac{x^2-x+1}{x^2+1} \cdot e^{\cot ^{-1} x} d x Put x=cot⁡t⇒−cosec⁡2tdt=dxx=\cot t \Rightarrow-\operatorname{cosec}^2 t d t=d x Now, 1+cot⁡2t=cosec⁡2t∴1+\cot ^2 t=\operatorname{cosec}^2 t\therefore\mathrm{I}=∫et(cot⁡2t−cot⁡t+1)(1+cot⁡2t)(−cosec⁡2t)dt=\int \frac{e^t\left(\cot ^2 t-\cot t+1\right)}{\left(1+\cot ^2 t\right)}\left(-\operatorname{cosec}^2 t\right) d t=−\intet(cosec⁡2t−cot⁡t)dt=\intet(\cott−cosec⁡2t)dt=etcot⁡t+C=ecot⁡−1x(x)+C≡A(x)\cdotecot⁡−1x+C⇒A(x)=x\begin{aligned}& =-\inte^t\left(\operatorname{cosec}{ }^2 t-\cot t\right) d t \\ & =\inte^t\left(\cott-\operatorname{cosec}^2 t\right) d t \\ & =e^t \cot t+\mathrm{C}\\ & =e^{\cot ^{-1} x}(x)+\mathrm{C} \equiv \mathrm{A}(x) \cdote^{\cot ^{-1} x}+\mathrm{C}\\ \Rightarrow \mathrm{A}(x) & =x \end{aligned}$
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