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Ldaniel
If f '(x) is defined for all x, then f(x) is defined for all x?
if f(x) is differentiable everywhere,,surely f(x) must be defined everywhere..
http://en.wikipedia.org/wiki/Differentiable_function#Differentiability_and_continuity "If ƒ is differentiable at a point [...], then ƒ must also be continuous at [the point]. " I can't remember what this was called.