Q: let f(x)=integral of e^(-t^2) limit from sin(x) to cos(x).Then find f'(pi/4)=
By making sure you integrate in an order that makes the problem tractable:
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There is a world of difference between double integrals and single integrals.
(I can't resist adding that you should have asked danny "How on erf do you do it?" .... Memo to baldeagle: I am the funniest )