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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Mathematics
Chapter
Indefinite Integration

NTA Abhyas 2020 · Mathematics · Indefinite Integration

The integral I = ∫ 2sin x (3 + 2x)dx simplifies to (where, C is the...

The integral I=∫2sinxI = ∫ 2sin x\left(3 + \sin 2x\right)dxsimplifiesto(where,simplifies to (where,C is the constant of integration)

Options

  1. Aln⁡∣2+sinx−cosx2−sinx+cosx∣−tan⁡−1(sinx+cosx)+C\ln \left|\dfrac{2 + sin x - cos x}{2 - sin x + cos x}\right| - \tan^{-1} \left(sin x + cos x\right) + C
  2. Bln⁡(sinx)+sin⁡2x+C\ln ( sin x ) + \sin 2x + C
  3. Csin⁡(2x)−ln⁡(cosx)+C\sin \left(2x\right) - \ln ( cos x ) + C
  4. D14ln⁡∣2+sinx−cosx2−sinx+cosx∣−12tan⁡−1(sinx+cosx2)+C\dfrac{1}{4}\ln \left|\dfrac{2 + sin x - cos x}{2 - sin x + cos x}\right| - \dfrac{1}{\sqrt{2}}\tan^{-1} \left(\dfrac{sin x + cos x}{\sqrt{2}}\right) + C

Correct answer

D. 14ln⁡∣2+sinx−cosx2−sinx+cosx∣−12tan⁡−1(sinx+cosx2)+C\dfrac{1}{4}\ln \left|\dfrac{2 + sin x - cos x}{2 - sin x + cos x}\right| - \dfrac{1}{\sqrt{2}}\tan^{-1} \left(\dfrac{sin x + cos x}{\sqrt{2}}\right) + C

Step-by-step solution

The given integral can be rewritten as,

I=∫sinx+cosx3+sin⁡2xdx+∫sinx−cosx3+sin⁡2xdxI = ∫ \dfrac{sin x + cos x}{3 + \sin 2x}dx + ∫ \dfrac{sin x - cos x}{3 + \sin 2x}dx
Let sinx−cosx=tsin x - cos x = t and sinx+cosx=usin x + cos x = u in 1st{1}^{st} and 2nd{2}^{nd} integral respectively.
∴I=∫dt4−t2−∫du2+u2∴ I = ∫ \dfrac{dt}{4 - t^{2}} - ∫ \dfrac{du}{2 + u^{2}}
=14ln⁡∣2+t2−t∣−12tan⁡−1(u2)+C= \dfrac{1}{4}\ln \left|\dfrac{2 + t}{2 - t}\right| - \dfrac{1}{2}\tan^{-1} \left(\dfrac{u}{2}\right) + C
Putting values of tt and uu, we get,

I=14ln⁡∣2+sin⁡x−cos⁡x2−sin⁡x+cos⁡x∣−12tan⁡−1(sin⁡x+cos⁡x2)+CI = \dfrac{1}{4}\ln \left|\dfrac{2 + \sin x - \cos x}{2 - \sin x + \cos x}\right| - \dfrac{1}{2}\tan^{-1} \left(\dfrac{\sin x + \cos x}{2}\right) + C

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