1. The problem statement, all variables and given/known data In the book it gave the example for standard change of variables as, z = x / 1 + x or equivalently x = z / 1 - z , then dx = dz / (1 - z)^2 , thus (2) 1 / (1 - z)^2 f (z / 1 - z) dz (3) This is what I am trying to accomplish but with the expression x^3 / (e^x - 1) dx. So I can put this expression equal to z and find equivalent equal to x then find dx eq(2) then final result eq (3). 2. Relevant equations integral of f(x) dx 3. The attempt at a solution I found the derivative to be (3*x^2/(e^x - 1)) - (x^3 * e^x / (e^x - 1)^2) but not getting the final result like in equation (3) from above maybe I am doing change of variables wrong. I have seen the formulas with variables online but still not getting it. If someone could help that would be GREAT!