# looking for some hard derivatives problem

I'm in the toughest school in my province and in enriched math course. We are learning derivatives and doing some hardcored stuff. Does anyone know any websites that have tons of good practices for derivatives?

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Why not just pick a random analysis textbook and see if you can find anything to suit your tastes among the exercises? – tomasz Oct 14 '12 at 17:58

Prove: $(fg)^{(n)}(x_0) = \sum{ {n \choose k} f^{(k)}(x_0)g^{(n-k)}(x_0)}$, $k$ runs from $0$ to $n$ in the sum.
provided $f$ and $g$ have $n$ derivatives at $x_0$.