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MathNet 2018-part-04 — 181 problems (EN–VI) Question 142

Math Olympiad Vault · MathNet 2018-part-04 — 181 problems (EN–VI)

Question 142

Let $\mathcal{F}$ be the set of continuous functions $f : \mathbb{R} \to \mathbb{R}$ which satisfy the condition
$$
e^{f(x)} + f(x) \geq x + 1,$$
for any real number $x$. Find the minimum value attained by the integral
$$
I(f) = \int_{0}^{e} f(x) \, dx,
$$
for $f$ lying in $\mathcal{F}$.