1. ## differentiability at x=0

A value of $k$ such that $f(x)= x^ k$ is $(n-1)$ -times

differentiable at $0$ but not $(n)$ -times differentiable at

$0$ is .

2. Hint:
$x^{4/3}$ is differentiable at 0.
$x^{1/3}$ is not differentiable at 0.