I am stuck on 4 problems involving a substitution to be solved.
It only says it must be solved using a substitution and no other method of solving integrals.
1) . I've trying a u-sub : , also and but in each case I failed to solve it.
2) . I don't really know what sub to make here. Maybe ?
3) . Making the sub , I got but I don't know how to finish it!
4) . I took and I got an answer very similar to the 3) : but don't know how to finish it.