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Explain Solution R.D.Sharma Class 12 Chapter 18 Indefinite Integrals Exercise Revision Exercise  Question 73 Maths Textbook Solution.

Answers (1)

Answer:

2\left(\frac{1}{\sqrt{3}}\right) \tan ^{-1} \frac{\left(\tan \left(\frac{x}{2}\right)\right)}{\sqrt{3}}

Hint:

To solve the given statement we will write \cos x \operatorname{as} \frac{1-\tan ^{2}\left(\frac{x}{2}\right)}{1+\tan ^{2}\left(\frac{x}{2}\right)}

Given:

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

Solution: 

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

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

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

I=2 \int \frac{d t}{t^{2}+(\sqrt{3})^{2}}

=2\left(\frac{1}{\sqrt{3}}\right) \tan ^{-1} \frac{\left(\tan \left(\frac{\mathrm{x}}{2}\right)\right)}{\sqrt{3}}

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