Which of the following function is not differentiable at x = 0?
1
f(x) = sin( |x|x )
2
\(f(x) =\begin{cases} sin(x^2) & if \ \ x\in \mathbb{Q} \\ 0 & otherwise\\ \end{cases}\)
3
\(f(x) =\begin{cases} sin(|x|) & if \ \ x\in \mathbb{Q} \\ 0 & otherwise\\ \end{cases}\)
4
f(x) = [x] sin2(πx) where [.] is greatest integer function