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The value of \(\int_{0}^{\pi} \frac{\sin x}{1 + \sin x}dx\) is equal to

  • A.\(\pi + 2\)
  • B.\(2\pi - 2\)
  • C.\(2\pi - 1\)
  • D.\(\pi - 2\)
  • E.\(\pi + 1\)

Answer: D

The value is \(\pi - 2\).

Write \(\frac{\sin x}{1 + \sin x} = 1 - \frac{1}{1 + \sin x}\).

\[ \begin{aligned} \int_{0}^{\pi}\frac{dx}{1 + \sin x} &= \int_{0}^{\pi}\frac{1 - \sin x}{\cos^{2}x}dx \\ &= \left[\tan x - \sec x\right]_{0}^{\pi} = 2 \\ \text{value} &= \pi - 2 \end{aligned} \]

The antiderivative \(\tan x - \sec x\) equals 1 at \(\pi\) and -1 at 0 (it is continuous across \(\frac{\pi}{2}\), with limit 0 there). \(\pi + 2\) adds instead of subtracting the second part.

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