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Explain solution RD Sharma class 12 chapter 19 Definite Integrals exercise Fill in the blanks question 12 maths

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Answer: \frac{1}{7}

Hint: You must know  \frac{d}{d x}(\tan x) \text { and } \int x^{n} d x

Given: \int_{0}^{\pi / 4} \tan ^{6} x \sec ^{2} x\; dx

Solution:  

I=\int_{0}^{\pi / 4} \tan ^{6} x \sec ^{2} x\; dx

Put

        \begin{aligned} &\tan x=t \\\\ &\sec ^{2} x \; d x=d t \end{aligned}

When \mathrm{x}=0, \mathrm{t}=0

When \mathrm{x}=\frac{\pi}{4}, \mathrm{t}=1

\begin{aligned} \mathrm{I} &=\int_{0}^{1} \mathrm{t}^{6} d t \\\\ &=\left[\frac{t^{7}}{7}\right]_{0}^{1} \end{aligned}

    \begin{aligned} &=\left[\frac{1}{7}-0\right] \\\\ &=\frac{1}{7} \end{aligned}

 

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