I am having a lot of trouble applying the product rule here. I have looked over the product rule but i find it very easy when I do it with the examples they provide me. This however is stumping me.

xc(px,py,U) = x[px,py,E(px,py,U)]

I need to partially differentiate this w.r.t px but I can't figue out how this applys to

f(x) = g(x)f(x) --> f'(x) = g'(x)f(x) + f'(x)g(x)

I know the answer because it has been drilled into my brain but I can't comprehend the working. Help me please?

sorry my formatting in word did not copy across. xc is meant to be x with c as a superscript. In this case it stands for x compensated.

Mr F edit:I think the OP means subscript, not superscript.