Question

Give an example which is continous everywhere but not differentiable at 3 points?

Answer 1

`f(x)=abs(x-1) * abs(x-2) * abs(x-3)`

Explanation:

Here is what a graph of this function would look like:
graph{abs(x-1)abs(x-2)abs(x-3) [-0.13, 4.736, -0.249, 2.181]}
Although the function is defined for `AAx in RR`
it is not differentiable at `x in {1,2,3}`