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Provide Solution for RD Sharma Class 12 Chapter 19 Definite Integrals Exercise Revision Exercise Question 37

Answers (1)

Answer:  \frac{\pi}{4}

Hint: To solve this equation we have to change cot into tan

Given:   \int_{0}^{\frac{\pi}{2}} \frac{1}{1+\cot ^{7} x} d x

Solution:

\int_{0}^{\frac{\pi}{2}} \frac{1}{1+\cot ^{7} x} d x=-\int_{0}^{\frac{\pi}{2}} \frac{1}{1+\frac{1}{\cot ^{7} x}} d x              I=\int_{0}^{\frac{\pi}{2}} \frac{\tan ^{7} x}{1+\tan ^{7} x} d x  ………….. (1)

I=\int_{0}^{\frac{\pi}{2}} \frac{1}{1+\cot \left(0+\frac{\pi}{2}-x\right)^{3}} d x

I=\int_{0}^{\frac{\pi}{2}} \frac{1}{1+\tan ^{7} x} d x  …….. (2)

Adding equation (1) and (2)

2 I=\int_{0}^{\frac{\pi}{2}} \frac{\tan ^{7} x}{1+\tan ^{7} x} d x+\int_{0}^{\frac{\pi}{2}} \frac{1}{1+\tan ^{7} x} d x

\begin{gathered} 2 I=\int_{0}^{\frac{\pi}{2}} d x \\ \end{gathered}

2 I=[x]_{0}^{\frac{\pi}{2}}

\begin{aligned} &2 I=\frac{\pi}{2}-0 \\ & \end{aligned}

I=\frac{\pi}{2 \times 2} \\

I=\frac{\pi}{4}

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