The set of all points where `f(x) = 2x|x|` is differentiable

The set of points where , f(x) = x|x| is twice differentiable is

The set of points where , f(x) = x|x| is twice differentiable is

The set of points where , f(x) = x|x| is twice differentiable is

The set of points where ,f(x)=x|x| is twice differentiable is

The set of points where f(x)=(x)/(1+|x|) is differentiable is

The set of points, where f(x)=(x)/(1+|x|) is differentiable, is :

The set of points where f(x)=x/(1+|x|) is differentiable is

Let f : R to R be a function defined by f(x) = max. {x, x^(3)} . The set of all points where f(x) is NOT differentiable is