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Need solution for RD Sharma maths class 12 chapter 19 Definite Integrals exercise Fill in the blanks question 15

Answers (1)

Answer: \frac{\pi }{4}

Hint: Use \int \frac{1}{1+x^{2}} d x

Given: \int_{0}^{\pi / 2} \frac{\sin x}{1+\cos ^{2} x} d x

Solution:  

\mathrm{I}=\int_{0}^{\pi / 2} \frac{\sin x}{1+\cos ^{2} x} \mathrm{dx}

Put 

        \begin{aligned} &\cos x=t \\\\ &-\sin x\; d x=d t \\\\ &\sin x \; d x=-d t \end{aligned}

When \mathrm{x}=0, \mathrm{t}=1

When \mathrm{x}=\frac{\pi}{2}, \mathrm{t}=0

\begin{aligned} \mathrm{I} &=-\int_{1}^{0} \frac{d t}{1+t^{2}} \\\\ &=\int_{0}^{1} \frac{d t}{1+t^{2}} \end{aligned}

    \begin{aligned} &=\left[\tan ^{-1} t\right]_{0}^{1} \\\\ &=\left[\tan ^{-1}(1)-\tan ^{-1}(0)\right] \\\\ &=\left[\tan ^{-1}\left(\tan \frac{\pi}{4}\right)-\tan ^{-1}(\tan 0)\right] \end{aligned}

    \begin{aligned} &=\left[\frac{\pi}{4}-0\right] \\\\ &=\frac{\pi}{4} \end{aligned}

 

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