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MathNet 2018-part-01 — 181 problems (EN–VI) Question 140

Math Olympiad Vault · MathNet 2018-part-01 — 181 problems (EN–VI)

Question 140

A point $X$ lies inside an isosceles right triangle $ABC$ with $\angle B = 90^\circ$.
Prove the inequality $AX + BX + \sqrt{2}CX \ge \sqrt{5}AB$ and find all points $X$ for which the equality holds.