If $f(x–y)= f(x)·g (y)–f (y)·g(x)$ and $g(x – y)=g(x)·g(y)+f(x)·f(y)$ for all $x, y \in R$. Find following for the following given conditions.
If $f$ and $g$ satisfy the sine/cosine addition formulae, then what is $g'(0)$?