We had a problem in class today which read
f(x) = x^2 if xЭQ
f(x) = 0 otherwise.
We are studying differentiability, and my tutor said that this function was differentiable at 0 but not at any other point.
I can see how to show its differentiable at 0, but I dont know how I would go about proving that is isn't differentiable at any other point.