Maybe this discussion will help.
http://math.stackexchange.com/questions/359023/using-the-limit-definition-to-find-the-derivative-of-ex
Givenƒ(x) = ex, verify that lim h->0 (e^x+h - e^h)/h + e^x and explain how this illustrates that ƒ′(x) = ln e • ƒ(x) = ƒ(x)
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