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π / 2 ∫ 0 sin 2 x log tan x d x is equal to

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Question

\[\int\limits_0^{\pi/2} \sin\ 2x\ \log\ \tan x\ dx\]  is equal to 

Options

  • π

  •  π/2

  •  0

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Solution

\[I = \int_0^\frac{\pi}{2} \sin2x \log \tan x\ d x . . . . . \left( 1 \right)\]

\[I = \int_0^\frac{\pi}{2} \sin\left( \pi - 2x \right) \log \tan\left( \frac{\pi}{2} - x \right) d x\]

\[I = \int_0^\frac{\pi}{2} \sin2x \log \cot x\ d x . . . . . \left( 2 \right)\]

\[\text{Adding} \left( 1 \right) and \left( 2 \right), \text{we get}, \]

\[2I = \int_0^\frac{\pi}{2} \sin2x\left( \log \tan x + \log \cot x \right) d x\]

\[2I = \int_0^\frac{\pi}{2} \sin2x\left( \log \tan x \cot x  \right) d x\]

\[2I = \int_0^\frac{\pi}{2} \sin2x\left( \log1 \right) d x\]

\[I = 0\]

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Chapter 19: Definite Integrals - MCQ [Page 120]

APPEARS IN

R.D. Sharma Mathematics Volume 1 and 2 [English] Class 12
Chapter 19 Definite Integrals
MCQ | Q 35 | Page 120

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