max function

Let f: R → R be a function such that f(x) = max{x,x³}, x ∈ R, where R is the set of all real numbers. The set of all points where f(x) is NOT differentiable is

Let $f : \mathbb{R} \rightarrow \mathbb{R}$ be a function such that $f(x) = \max \{x, x^3\}, x \in \mathbb{R}$, where $\mathbb{R}$ is the set of all real numbers. The set of all po...