Determine whether or not the derivative for the function f(x) below exists at x=0. Find f'(x) if exists.

f(x) = { x^3 * cos (1/x) if x != 0

{ 0 if x = 0

I'm sorry for being stupid. I personally think this problem is not hard

And also I don't know how to do math code so forgive me

Thank you in advance.