IMC 1994 · Problem 2

Day 113 points1st IMC · Plovdiv, Bulgaria

Statement

Let fC1(a,b)f \in C^1(a,b), limxa+f(x)=+\lim\limits_{x \to a+} f(x) = +\infty, limxbf(x)=\lim\limits_{x \to b-} f(x) = -\infty and f(x)+f2(x)1f'(x) + f^2(x) \ge -1 for x(a,b)x \in (a,b). Prove that baπb - a \ge \pi and give an example where ba=πb - a = \pi.

Official solution

Hidden so you can work on the problem first.