I was given this problem in my calculus class and I have ablsolutely no idea how to solve it. Any help would be greatly appreciated.

Consider the two functions F and G whose derivates Fprime and Gprime exist. the functions have the properties listed below for all values of x. Prove Gprime(x)=-F(x)

I. (F(x))^2 + (G(x))^2=1

II. Fprime(x)=G(x)

III. G(x)>0

IV. F(0)=0