I have and I must find . I'm asking you to help me finding the inverse function of f, I'll try to do the derivative.

One of my guesses would be that as I have an integral of a function, the inverse operation is the derivative of the integral. In other words I would say that maybe the inverse function of is . But looking back, if I replace this in the upper limit of the integral of , I doubt it will give me the identity. I also know that is . Hmm... can you help me a bit?