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MathNet 2020 — Math Olympiad Vault — Part 05 Question 55

Math Olympiad Vault · MathNet 2020 — Math Olympiad Vault — Part 05

Question 55

In square $ABCD$, points $M,N$ lie in the interiors of sides $BC,CD$ respectively, with $\angle MAN=45^\circ$. Let $O$ be the intersection of the circle through $C,M,N$ with segment $AC$.

Question illustration

a) Prove that $OM=ON$.

b) Prove that $O$ is the center of the circle through $A,M,N$.