I've got this problem:

f(y) = , y>0

0, elsewhere

Now I'm supposed to find for any positive integer k.

I start out like this:

= =

I then move out and m outside the integral =

=

and from here I don't know how to go on. The correct answer is

and I know that

but I don't see how can be rewritten to the correct answer. Thanks in advance for your help.