1. ## integral

$\int{x^3cos^2(x^2)dx}=$

substitute: $u=x^2$, $du=2xdx$

$\frac{1}{2}\int ucos^2u du$

i need help solving this from here

2. Use $\cos^2u=1-\sin^2u$

You'll have an integral to compute applying integration by parts.

You can use too $\cos^2u=\frac12(1+\cos2u)$