Let f(x) be a real valued function defined for all x >= 1, that satisfies
f(1) = 1 and
f'(x) = 1/[x^2 + (f(x))^2]
Prove that lim f(x) as x tends to infinity exists and is less than 1+ pi/4.
Suppose that a continuously differentiable function f : IR --IR satisfies
f'(x) = g(f(x)) + h(x) for x in IR,
where the functions g, h : IR ---IR are C 00 (i.e. infinitely differentiable). Prove that
the function f is infinitely differentiable as well.