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  • Provide Solution For R.D.Sharma Maths Class 12 Chapter 18 Indefinite Integrals Exercise 18.3 Question 13 Maths Textbook Solution.

Provide Solution For  R.D.Sharma Maths Class 12 Chapter 18  Indefinite Integrals Exercise 18.3 Question 13 Maths Textbook Solution.

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Answer: \frac{1}{3}\left[\frac{1-\cos 3 x}{\sin 3 x}\right]+C

Hint: \text { We will add } 1-\cos 3 x \text { to the equation }

Given: \int \frac{1}{1+\cos 3 x} d x

Solution: \int \frac{1}{1+\cos 3 x} d x

\text { Multiplying } 1-\cos 3 x \text { in numerator and denominator }

\begin{aligned} &\int \frac{1-\cos 3 x}{(1+\cos 3 x)(1-\cos 3 x)} d x \\ &=\int \frac{1-\cos 3 x}{1-\cos ^{2} 3 x} d x \\ &=\int \frac{1-\cos 3 x}{\sin ^{2} 3 x} d x \end{aligned}

\begin{aligned} &=\int \frac{1}{\sin ^{2} 3 x} d x-\int \frac{\cos 3 x}{\sin 3 x \sin 3 x} d x \\ &=\int \operatorname{cosec}^{2} 3 x d x-\int \cot 3 x \operatorname{cosec} 3 x d x \\ &=\frac{-\cot 3 x}{3}+\frac{\operatorname{cosec} 3 x}{3}+c \end{aligned}

\begin{aligned} &=\frac{1}{3}[\operatorname{cosec} 3 x-\cot 3 x]+c \\ &=\frac{1}{3}\left[\frac{1}{\sin 3 x}-\frac{\cos 3 x}{\sin 3 x}\right]+C \\ &=\frac{1}{3}\left[\frac{1-\cos 3 x}{\sin 3 x}\right]+C \end{aligned}

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