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MathNet 2016-part-04 — 184 problems (EN–VI) Question 49

Math Olympiad Vault · MathNet 2016-part-04 — 184 problems (EN–VI)

Question 49

The right isosceles triangle $ABC$ has $m(\angle A) = 90^\circ$. Take $M \in (BC)$ so that $m(\angle AMB) = 75^\circ$ and take $F$ on the internal bisector of the angle $MAC$ so that $BF = AB$. Prove that:

a) the lines $AM$ and $BF$ are perpendicular;

b) the triangle $CFM$ is isosceles.