ok, this definition of f is just a bunch of points (4 to be exact).
so if point (a,b) is part of f, then f(a)=b
f(1) is about point (1,0), so f(1)=0.
g(1) = 1 (due to point (1,1))
g(2/3) = 0
f(2) = 3/4
g(-2) = 3
f(π) = -2
just a lookup once you see what is happening