This is probably what he was referring to:
Differentiation under the integral sign - Wikipedia, the free encyclopedia
Like in this thread...
http://www.mathhelpforum.com/math-he...-integral.html
From simplependulums post.
I've seen it used in another thread as well.
What is it?
This is probably what he was referring to:
Differentiation under the integral sign - Wikipedia, the free encyclopedia