IMC 2023 · Problem 7

Day 230th IMC · Blagoevgrad, Bulgaria

Statement

Let VV be the set of all continuous functions f ⁣:[0,1]Rf \colon [0, 1] \to \mathbb{R}, differentiable on (0,1)(0, 1), with the property that f(0)=0f(0) = 0 and f(1)=1f(1) = 1. Determine all αR\alpha \in \mathbb{R} such that for every fVf \in V, there exists some ξ(0,1)\xi \in (0, 1) such that

f(ξ)+α=f(ξ).f(\xi) + \alpha = f'(\xi).

Official solution

Hidden so you can work on the problem first.

Proposed by Mike Daas, Leiden University.