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MathNet 2019-part-07 — 184 problems (EN–VI) Question 55

Math Olympiad Vault · MathNet 2019-part-07 — 184 problems (EN–VI)

Question 55

In a right triangle $ABC$ with $\angle ACB = 90^\circ$ let $D$ be the foot of the altitude from $C$. Let $E$ and $F$ be the reflections of $D$ with respect to $AC$ and $BC$, respectively. Let $O_1$ and $O_2$ be the circumcenters of the triangles $ECB$ and $FCA$, respectively. Prove that
$$
2|O_1O_2| = |AB|.
$$