This is the well-known Dirichlet function: Math Tutor - Functions - Theory - Elementary Functions
Let, f(x) = x , if x is rational
= 0 , if x is irrational.
Then at x=0, which one of he followings is true?
(a) both f and are differentiable
(b) neither f nor are differentiable
(c) is continuous but not differentiable
(d) is differentiable but f is not
please help.
This is the well-known Dirichlet function: Math Tutor - Functions - Theory - Elementary Functions