IMC 1994 · Problem 2

Day 113 points1st IMC · Plovdiv, Bulgaria

Statement

Let f∈C1(a,b)f \in C^1(a,b), lim⁡x→a+f(x)=+∞\lim\limits_{x \to a+} f(x) = +\infty, lim⁡x→b−f(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 b−a≥πb - a \ge \pi and give an example where b−a=πb - a = \pi.

Official solution

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