Trigonometric Functions | Fundamental Integration Formulas

Basic Formulas

1. $ \displaystyle \int \sin u \, du = -\cos u + C $

2. $ \displaystyle \int \cos u \, du = \sin u + C $

3. $ \displaystyle \int \sec^2 u \, du = \tan u + C $

4. $ \displaystyle \int \csc^2 u \, du = -\cot u + C $

5. $ \displaystyle \int \sec u \, \tan u \, du = \sec u + C $

6. $ \displaystyle \int \csc u \, \cot u \, du = -\csc u + C $
 

Formulas Derived from Logarithmic Function

7. $ \displaystyle \int \tan u \, du = \ln (\sec u) + C = -\ln (\cos u) + C $

8. $ \displaystyle \int \cot u \, du = \ln (\sin u) + C $

9. $ \displaystyle \int \sec u \, du = \ln (\sec u + \tan u) + C $

10. $ \displaystyle \int \csc u \, du = \ln (\csc u - \cot u) + C = -\ln (\csc u + \cot u) + C $
 
The six basic formulas for integration involving trigonometric functions are stated in terms of appropriate pairs of functions. An integral involving $ \sin x $ and $ \tan x $, which the simple integration formula cannot be applied, we must put the integrand entirely in terms of $ \sin x $ and $ \cos x $ or in terms of $ \tan x $ and $ \sec x $. Notice that these formulas are reverse formulas in Differential Calculus.
 
The formulas derived from trigonometric function can be traced as follows:
 
$ \displaystyle \int \tan u \, du $

$ \,\,\,\,\,\,\,\,\, = \displaystyle \int \dfrac{\sin u \, du}{\cos u} $

$ \,\,\,\,\,\,\,\,\, = -\displaystyle \int \dfrac{-\sin u \, du}{\cos u} $

$ \,\,\,\,\,\,\,\,\, = -\ln (\cos u) + C $            → Formula

$ \,\,\,\,\,\,\,\,\, = \ln (\cos u)^{-1} + C $

$ \,\,\,\,\,\,\,\,\, = \ln \left(\dfrac{1}{\cos u} \right) + C $

$ \,\,\,\,\,\,\,\,\, = \ln (\sec u) + C $            → Formula
 

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