Show that f is not differentiable at 0

Hey guys, I need help with this question that has been bugging me...

Let f(x) = x^{3/5}. Show that f is not differentiable at zero. Show that y = x^{3/5} has a vertical tangent line at (0,0)

I don't know how to prove the statements... Any tips and pointers (plus the method) will help alot...

Thanks!

Re: Show that f is not differentiable at 0

There are several **different** ways to do this, depending on what you can or want to use.

Of course, a function of one variable **is** "differentiable" at x= a if and only if exists. It is NOT differentiable if that limit does not exist. So you could show that does not exist.

Or you could use the fact that, while the derivative of a function is not necessarily continuous, it **does** have the "intermediate value property". In particular, if the derivative at x= a exists, then . So what **is** the derivative of ? What is the limit of that derivative as x goes to 0?