Evaluate the integral `int_0^(pi/2) sin^5x dx`

The integral
`int_0^(pi/2) sin^5x dx` has to be determined.

 `int sin^5x dx`

=> `int sinx*sin^4x dx`

=> `int sinx*(1 - cos^2x)^2
dx`

let `cos x = y` , `dy = -sin x dx`

=> `-int (1
-...