# ∫ 1 2 + Cos X Dx - Mathematics

Sum

$\int\frac{1}{2 + \cos x} \text{ dx }$

#### Solution

$\text{ Let I } = \int\frac{1}{2 + \cos x}dx$
$\text{ Putting cos x }= \frac{1 - \tan^2 \frac{x}{2}}{1 + \tan^2 \frac{x}{2}}$
$\therefore I = \int\frac{1}{2 + \left( \frac{1 - \tan^2 \frac{x}{2}}{1 + \tan^2 \frac{x}{2}} \right)}dx$
$= \int\frac{\left( 1 + \tan^2 \frac{x}{2} \right)}{2 \left( 1 + \tan^2 \frac{x}{2} \right) + 1 - \tan^2 \left( \frac{x}{2} \right)}dx$
$= \int\frac{\sec^2 \left( \frac{x}{2} \right)}{2 + 2 \tan^2 \left( \frac{x}{2} \right) + 1 - \tan^2 \left( \frac{x}{2} \right)}dx$
$= \frac{\sec^2 \left( \frac{x}{2} \right)}{3 + \tan^2 \left( \frac{x}{2} \right)}dx$
$\text{ Putting tan } \frac{x}{2} = t$
$\Rightarrow \frac{1}{2} \text{ sec }^2 \left( \frac{x}{2} \right) dx = dt$
$\Rightarrow \text{ sec}^2 \left( \frac{x}{2} \right) dx = \text{ 2 dt }$
$\therefore I = \int\frac{2}{3 + t^2} \text{ dt}$
$= 2\int\frac{1}{t^2 + \left( \sqrt{3} \right)^2}dt$
$= \frac{2}{\sqrt{3}} \text{ tan}^{- 1} \left( \frac{t}{\sqrt{3}} \right) + C$
$= \frac{2}{\sqrt{3}} \text{ tan}^{- 1} \left( \frac{\tan \frac{x}{2}}{\sqrt{3}} \right) + C............ \left[ \because t = \tan \frac{x}{2} \right]$

Concept: Indefinite Integral Problems
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#### APPEARS IN

RD Sharma Class 12 Maths
Chapter 19 Indefinite Integrals
Revision Excercise | Q 73 | Page 204