`text(Introduction)`
By now you should be well aware of the important results that
`int cos kx dx =1/k sin kx + c \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ int sin kx dx = −1/k cos kx + c`
However, a little more care is needed when we wish to integrate more complicated trigonometric functions such as `int sin2 x dx, intsin 3x cos 2x dx`, and so on. In case like these trigonometric identities can be used to write the integrand in an alternative form which can be integrated more readily.

`text(Integrals requiring the use of trigonometric identities)`
The trigonometric identities are summarised here:
`2 sin A cos B = sin(A + B) + sin(A − B)`

`2 cos A cos B = cos(A − B) + cos(A + B)`

`2 sin A sin B = cos(A − B) − cos(A + B)`

`sin^2 A + cos^2 A = 1`

`cos 2A = cos2 A − sin2 A`
`quadquadquadquadquadquad= 2 cos2 A − 1`
`quadquadquadquadquadquad= 1 − 2 sin2 A`

`sin 2A = 2 sin A cos A`

`1 + tan2 A = sec2 A`