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Need Solution for R.D.Sharma Maths Class 12 Chapter 18 Indefinite Integrals Exercise Revision Exercise Question 64 Maths Textbook Solution.

Answers (1)

Answer:

I=\frac{1}{\sqrt{3}} \ln \left|\frac{\sqrt{3}+\tan \left(\frac{x}{2}\right)}{\sqrt{3}-\tan \left(\frac{x}{2}\right)}\right|+c

Hint

We will write \cos x \operatorname{as}\left(\frac{1-\tan ^{2} \frac{x \lambda}{2}}{1+\tan ^{2} \frac{x}{2}}\right)

Given:

\int \frac{1}{1+2 \cos x} d x

Solution:

I=\int \frac{1}{1+2 \cos x} d x

    I=\int \frac{1}{1+2\left(\frac{1-\tan ^{2 \frac{x}{2}}}{1+\tan ^{2} \frac{x}{2}}\right)} d x

I=\int \frac{1+\tan ^{2} \frac{x}{2}}{1+\tan ^{2} \frac{x}{2}+2-2 \tan ^{2} \frac{x}{2}} d x

I=\int \frac{\sec ^{2} \frac{x}{2}}{3-\tan ^{2} \frac{x}{2}} d x

I=\int \frac{2 d t}{3-t^{2}}                                                \left[\because \tan \frac{\mathrm{x}}{2}=t, d t=\sec ^{2}\left(\frac{x}{2}\right)\left(\frac{1}{2}\right) d x\right]

I=2 \int \frac{d t}{(\sqrt{3})^{2}-t^{2}}                                \left[\because \sec ^{2}\left(\frac{x}{2}\right) d x=2 d t\right]

I=2\left(\frac{1}{2 \sqrt{3}}\right) \ln \left|\frac{\sqrt{3}-t}{\sqrt{3}+t}\right|+c

I=\frac{1}{\sqrt{3}} \ln \left|\frac{\sqrt{3}+t}{\sqrt{3}-t}\right|+c

I=\frac{1}{\sqrt{3}} \ln \left|\frac{\sqrt{3}+\tan \left(\frac{x}{2}\right)}{\sqrt{3}-\tan \left(\frac{x}{2}\right)}\right|+c

 

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