English

2 π ∫ 0 Cos 7 X D X

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Question

\[\int\limits_0^{2\pi} \cos^7 x dx\]

Sum
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Solution

\[Let, I = \int_0^{2\pi} \cos^7 x d x ..............(1)\]

\[ = \int_0^{2\pi} \cos^7 \left( 2\pi - x \right) d x\]

\[ = \int_0^{2\pi} - \cos^7 x d x\]

\[ \Rightarrow I = - \int_0^{2\pi} \cos^7 x d x ..............(2)\]

Adding (1) and (2) we get,

\[ 2I = \int_0^{2\pi} \cos^7 x d x - \int_0^{2\pi} \cos^7 x d x\]

\[ \Rightarrow 2I = 0\]

\[ \therefore I = 0\]

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Chapter 19: Definite Integrals - Revision Exercise [Page 122]

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R.D. Sharma Mathematics Volume 1 and 2 [English] Class 12
Chapter 19 Definite Integrals
Revision Exercise | Q 38 | Page 122

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