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Oct15-10, 12:49 PM
P: 273
Sorry its been a while, I've been rather busy with midterms. So I suppose also (contraspositive) that if not all directional derivatives exist at a point then the function is not differentiable at the point right?

Btw, geometrically what is the directional derivative of a function f: R -> R? Is it like the slope of a messed up tangnet? That's what it seems like..