Question:

Find the integrals of the function: \(\frac{cos x}{1+cos x}\)

Updated On: Oct 19, 2023
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Solution and Explanation

\(\frac{cos x}{1+cos x}\) = \(\frac{cos^2   (\frac{x}{2})  -sin^2   (\frac{x}{2})  }{2cos^2   (\frac{x}{2})       }\)                            [cos x= cos2 \(\frac{x}{2}\)-sin2 \(\frac{x}{2}\) and cos x = 2cos2 \(\frac{x}{2}\)-1]
=\(\frac{1}{2}\)[1-tan2 \(\frac{x}{2}\)]
∴ ∫\(\frac{cos x}{1+cos x}dx\) = \(\frac{1}{2}\)∫(1-tan2\(\frac{x}{2}\))dx
\(\frac{1}{2}\) ∫(1-sec2 \(\frac{x}{2}\)+1)dx
\(\frac{1}{2}\)∫(2-sec2 \(\frac{x}{2}\))dx
\(\frac{1}{2}\)[\(2x-\frac{tan(\frac{x}{2})}{(\frac{1}{2})}\)]+C
=x -tan\(\frac{x}{2}\)+C
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Concepts Used:

Methods of Integration

Given below is the list of the different methods of integration that are useful in simplifying integration problems:

Integration by Parts:

 If f(x) and g(x) are two functions and their product is to be integrated, then the formula to integrate f(x).g(x) using by parts method is:

∫f(x).g(x) dx = f(x) ∫g(x) dx − ∫(f′(x) [ ∫g(x) dx)]dx + C

Here f(x) is the first function and g(x) is the second function.

Method of Integration Using Partial Fractions:

The formula to integrate rational functions of the form f(x)/g(x) is:

∫[f(x)/g(x)]dx = ∫[p(x)/q(x)]dx + ∫[r(x)/s(x)]dx

where

f(x)/g(x) = p(x)/q(x) + r(x)/s(x) and

g(x) = q(x).s(x)

Integration by Substitution Method

Hence the formula for integration using the substitution method becomes:

∫g(f(x)) dx = ∫g(u)/h(u) du

Integration by Decomposition

Reverse Chain Rule

This method of integration is used when the integration is of the form ∫g'(f(x)) f'(x) dx. In this case, the integral is given by,

∫g'(f(x)) f'(x) dx = g(f(x)) + C

Integration Using Trigonometric Identities