int x^2 cos x dx let u= x^2:. du = 2x dx
dv = cosx dx or int dv = int cos x dx or v = sin x
int x^2 cos x dx = uv - int v du = x^2 sin x - int sinx *2x dx or
int x^2 cos x dx =x^2 sin x - 2int sinx *x dx
let u= x:. du = dx ,dv = sin x dx or v = -cos x
int sinx *x dx = - x cos x - int -cosx dx or
int sinx *x dx = - x cos x + int cosx dx or
int sinx *x dx = - x cos x + sinx
int x^2 cos x dx =x^2 sin x - 2(- x cos x + sin x ) or
int x^2 cos x dx =x^2 sin x + 2 x cos x - 2 sin x + c [Ans]