We want to show that f(g(x)) = x and g(f(x)) = x.
So to do that, we need to calculate f(g(x)) and g(f(x)) explicitly.
Let's begin with f(g(x))
Now, f(g(x)) = f(4/x), by definition of g, as g(x) = 4/x
What then is f(4/x) equal to? Use the definition of f.
