The question:

Let f(x,y) be a differentiable function at (0,0) that satisfies f(0,0)=0.

Let be a differentiable function at t=0 that satisfies:

and let .

Prove g is differentiable at (0,0) and that .

My try:

We know the two functions are differentiable at (0,0) , hence:

and:

So:

From that point I'm pretty stuck...I can't understand how to continue solving the question...

I'll be delighted to get some guidance

Thanks !