I'm trying to prove that f(r,s)=(r*cos(s),r*sin(s)) is differentiable using the definition of the Frechet derivative, that is:

$\displaystyle \lim_{h \to 0} \frac{ \| f(x + h) - f(x) - L*h \|}{ \|h\|} = 0 $

I know how to calculate the Frechet derivative, but I'm not sure how to "show that it's differentiable" using the above definition.