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NDA 2020
Exam
NDA
Year
2020
Subject
Mathematics
Chapter
Indefinite Integration

NDA 2020 · Mathematics · Indefinite Integration

What is ∫(e^ x + x) x d x equal to ?

What is ∫(elog⁡x+sin⁡x)cos⁡xdx\int\left(e^{\log x}+\sin x\right) \cos x d x equal to ?

Options

  1. Asin⁡x+xcos⁡x+sin⁡2x2+c\sin x+x \cos x+\frac{\sin ^2 x}{2}+c
  2. Bsin⁡x−xcos⁡x+sin⁡2x2+c\sin x-x \cos x+\frac{\sin ^2 x}{2}+c
  3. Cxsin⁡x+cos⁡x+sin⁡2x2+cx \sin x+\cos x+\frac{\sin ^2 x}{2}+c
  4. Dxsin⁡x−xcos⁡x+sin⁡2x2+cx \sin x-x \cos x+\frac{\sin ^2 x}{2}+c

Correct answer

C. xsin⁡x+cos⁡x+sin⁡2x2+cx \sin x+\cos x+\frac{\sin ^2 x}{2}+c

Step-by-step solution

∫(elog⁡x+sin⁡x)⋅cos⁡x⋅dx=∫(x+sin⁡x)⋅cos⁡x⋅dx=∫(x⋅cos⁡x+sin⁡x⋅cos⁡x)⋅dx\begin{aligned} & \int\left(e^{\log x}+\sin x\right) \cdot \cos x \cdot d x=\int(x+\sin x) \cdot \cos x \cdot d x \\ & =\int(x \cdot \cos x+\sin x \cdot \cos x) \cdot d x\end{aligned}=∫x⋅cos⁡x⋅dx+∫sin⁡x⋅cos⁡x⋅dx=x⋅∫cos⁡x⋅dx−∫(dxdx⋅∫(cos⁡x)⋅dx)⋅dx+∫sin⁡x⋅cos⁡x⋅dx\begin{aligned} & =\int x \cdot \cos x \cdot d x+\int \sin x \cdot \cos x \cdot d x \\ & =x \cdot \int \cos x \cdot d x-\int\left(\frac{d x}{d x} \cdot \int(\cos x) \cdot d x\right) \cdot d x \\ & \quad+\int \sin x \cdot \cos x \cdot d x\end{aligned}=x⋅sin⁡x−∫sin⁡x⋅dx+∫sin⁡x⋅cos⁡x⋅dx=x⋅sin⁡x−(−cos⁡x)+∫sin⁡x⋅cos⁡x⋅dx\begin{aligned} & =x \cdot \sin x-\int \sin x \cdot d x+\int \sin x \cdot \cos x \cdot d x \\ & =x \cdot \sin x-(-\cos x)+\int \sin x \cdot \cos x \cdot d x\end{aligned}=x \sin x+\cos x+\int \sin x \cdot \cos x \cdot d xNow,Now,\int \sin x \cdot \cos x \cdot d xLetLet\sin x=z, d z=\cos x \cdot d x\int \sin x \cdot \cos x d x=\int z \cdot d z=\frac{z^2}{2}=\frac{\sin ^2 x}{2}\therefore I=x \cdot \sin x+\cos x+\frac{\sin ^2 x}{2}+C$
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