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MathNet 2017-part-05 — 176 problems (EN–VI) Question 6

Math Olympiad Vault · MathNet 2017-part-05 — 176 problems (EN–VI)

Question 6

On the side $[CD]$ of the square $ABCD$ point $E$ is chosen such that $m(\angle ABE) = 60^{\circ}$. On the halfline $(BA$ point $F$ is chosen such that $[BE] = [BF]$. Let $M$ be the intersection between the lines $EF$ and $AD$.

a) Prove that $m(\angle BME) = 75^{\circ}$.

b) The bisector of angle $CBE$ intersects $CD$ at $N$. Prove that the triangle $BMN$ is equilateral.

Question illustration