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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Indefinite Integration

NDA 2025 · Mathematics · Indefinite Integration

For the following two (02) items: Let u = ∫ e^x x\, dx and v = ∫...

For the following two (02) items:
Let u=∫excos⁡x dxu = \int e^x \cos x\, dx and v=∫exsin⁡x dxv = \int e^x \sin x\, dx.

Consider the following:
I. dudx=−v\dfrac{du}{dx} = -v
II. dvdx=−u\dfrac{dv}{dx} = -u
Which of the above is/are correct?

Options

  1. AI only
  2. BII only
  3. CBoth I and II
  4. DNeither I nor II

Correct answer

D. Neither I nor II

Step-by-step solution

Given u=∫excos⁡x dxu = \int e^x \cos x\, dx and v=∫exsin⁡x dxv = \int e^x \sin x\, dx.

Differentiating both sides with respect to xx, we get:
dudx=excos⁡x\dfrac{du}{dx} = e^x \cos x
dvdx=exsin⁡x\dfrac{dv}{dx} = e^x \sin x

Evaluating the integrals, we have:
u=ex2(cos⁡x+sin⁡x)+C1u = \dfrac{e^x}{2}(\cos x + \sin x) + C_1
v=ex2(sin⁡x−cos⁡x)+C2v = \dfrac{e^x}{2}(\sin x - \cos x) + C_2

Comparing the derivatives with uu and vv, it is clear that:
dudx≠−v\dfrac{du}{dx} \neq -v
dvdx≠−u\dfrac{dv}{dx} \neq -u

Therefore, neither statement I nor statement II is correct.
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