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JEE Main 201412 AprilOnline
Exam
JEE Main
Year
2014
Date
12 April
Mode
Online
Subject
Mathematics
Chapter
Indefinite Integration

JEE Main 2014 · 12 April · Online · Mathematics · Indefinite Integration

The integral ∫ ( ^2 x ^2 x)/( ( ^3 x+ ^3 x)^2) d x is equal to:

\text{ The integral } \int \frac{\sin ^2 x \cos ^2 x}{\left(\sin ^3 x+\cos ^3 x\right)^2}d x  is equal to: \text{ is equal to: }

Options

  1. A1(1+cot⁡3x+c\frac{1}{\left(1+\cot ^3 x\right.}+c
  2. B−13(1+tan⁡3x+c)\left.-\frac{1}{3\left(1+\tan ^3 x\right.}+c\right)
  3. Csin⁡3x(1+cos⁡3x+c\frac{\sin ^3 x}{\left(1+\cos ^3 x\right.}+c
  4. D−cos⁡3x3(1+sin⁡3x+c-\frac{\cos ^3 x}{3\left(1+\sin ^3 x\right.}+c

Correct answer

B. −13(1+tan⁡3x+c)\left.-\frac{1}{3\left(1+\tan ^3 x\right.}+c\right)

Step-by-step solution

Let I=∫sin⁡2xcos⁡2x(sin⁡3x+cos⁡3x)2dxI=\int \frac{\sin ^2 x \cos ^2 x}{\left(\sin ^3 x+\cos ^3 x\right)^2} d xI=∫(sin⁡x⋅cos⁡xsin⁡3x+cos⁡3x)2dxI=∫(sin⁡x⋅cos⁡xcos⁡3x(1+tan⁡3x))2dx=∫(sin⁡x⋅sec⁡2x(1+tan⁡3x))2dx Put 1+tan⁡3x=tdt=3tan⁡2xsec⁡2xdx or dx=dt3tan⁡2xsec⁡2x∴I=∫sin⁡2x⋅sec⁡4xt2×dt3tan⁡2xsec⁡2x\begin{aligned}&\mathrm{I}=\int\left(\frac{\sin x \cdot \cos x}{\sin ^3 x+\cos ^3 x}\right)^2 d x \\ &\mathrm{I}=\int\left(\frac{\sin x \cdot \cos x}{\cos ^3 x\left(1+\tan ^3 x\right)}\right)^2 d x \\ &=\int\left(\frac{\sin x \cdot \sec ^2 x}{\left(1+\tan ^3 x\right)}\right)^2 d x \\ &\text{ Put }1+\tan ^3 x=\mathrm{t}\\ &d t=3 \tan ^2 x \sec ^2 x d x \text{ or }d x \\ &=\frac{d t}{3 \tan ^2 x \sec ^2 x}\\ &\therefore \mathrm{I}=\int \frac{\sin ^2 x \cdot \sec ^4 x}{t^2} \times \frac{d t}{3 \tan ^2 x \sec ^2 x} \end{aligned}I=13∫sin⁡2x⋅sec⁡4xt2×dtsin⁡2xcos⁡2x×sec⁡2x=13∫sin⁡2x⋅sec⁡4xt2×dtsin⁡2xsec⁡4x∴I=13∫dtt2=13\intt−2dtI=13[t−2+1−2+1]+c=−13[1t]+c or I=−13(1+tan⁡3x)+c\begin{aligned}&\mathrm{I}=\frac{1}{3} \int \frac{\sin ^2 x \cdot \sec ^4 x}{t^2} \times \frac{d t}{\frac{\sin ^2 x}{\cos ^2 x} \times \sec ^2 x}\\ &=\frac{1}{3} \int \frac{\sin ^2 x \cdot \sec ^4 x}{t^2} \times \frac{d t}{\sin ^2 x \sec ^4 x}\\ &\therefore \mathrm{I}=\frac{1}{3} \int \frac{d t}{t^2}=\frac{1}{3} \intt^{-2} d t \\ &\mathrm{I}=\frac{1}{3}\left[\frac{t^{-2+1}}{-2+1}\right]+c=\frac{-1}{3}\left[\frac{1}{t}\right]+c \\ &\text{ or } \mathrm{I}=-\frac{1}{3\left(1+\tan ^3 x\right)}+c \end{aligned}$
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