If `f(x)+f(y)=f((x+y)/(1-x y))` and `f'(0)=3,` then `f(tan(1/3))` must be equals to

Given that f(x) is a differentiable function of x and that f(x) ,f(y) = f(x) + f(y) +f(xy) -2 and that f(1)=2 , f(2) = 5 Then f(3) is equal to

If f(x)=3^(1+x)," then "f(x)f(y)f(z) is equal to

f(x+y)=f(x).f(y) for all x,yinR and f(5)=2,f'(0)=3 then f'(5) is equal to

Let f(x+y)=f(x)*f(y) for all x y where f(0)!=0 .If f(5)=2 and f'(0)=3 then f'(5) is equal to