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Explain Solution R.D. Sharma Class 12 Chapter 18 Indefinite Integrals Exercise Revision Exercise  Question 27 Maths Textbook Solution.

Answers (1)

Answer:

\frac{1}{2 \sqrt{2}} \log \left|\frac{\sqrt{2} \cos x+1}{\sqrt{2} \cos x-1}\right|+c

Given:

\int \frac{\sin x}{\cos 2 x} d x

Hint:

To solve the equation we will use substitution method.

Solution: 

I=\int \frac{\sin x}{\cos 2 x} d x

    =\int \frac{\sin x}{2 \cos ^{2} x-1} d x

I=-\int \frac{d t}{2 t^{2}-1} \ldots[\mathrm{put} \cos \mathrm{x}=\mathrm{t},-\sin x \mathrm{dx}=\mathrm{d} \mathrm{t}]

I=\frac{1}{2} \int \frac{d t}{\frac{1}{2}-t^{2}}

I=-\frac{1}{2} \int \frac{d t}{t^{2}-\left(\frac{1}{\sqrt{2}}\right)^{2}}

I=-\frac{1}{2} \frac{\sqrt{2}}{2} \log \left|\frac{t-\frac{1}{\sqrt{2}}}{t+\frac{1}{\sqrt{2}}}\right|+c

I=\frac{1}{2 \sqrt{2}} \log \left|\frac{\sqrt{2} \cos x+1}{\sqrt{2} \cos x-1}\right|+\mathrm{C}

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