The expression for the Gamma function is given as:

for Re(z)>0, and we change the variable into

for .

It then says that by this, we get:

Which I am not sure how they got.

Here is what I tried:

Given

Then I assume and

Substituting variables, I get:

Which is not the same as what I'm suppose to get.

If someone could show how it should be done, that would be greatly appreciated.

Thank you.