When the integrand involves some trigonometric functions, we use some known identities to find the integral as following example.
i) `int cos x^2` dx
⇒ cos 2x = 2 `cos^2 x` – 1, which gives
`cos^2x = (1+cos 2x )/2`
`int cos^2x dx = 1/2 int (1+ cos 2x)dx =1/2 int dx + 1/2 int cos 2x dx`
=`x/2 +1/4 sin 2x + C`