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MathNet 2026 — Part 10 Question 69

Math Olympiad Vault · MathNet 2026 — Part 10

Question 69

In triangle $ABC$, $\angle A = 50^\circ$, $\angle B = 60^\circ$, and $\angle C = 70^\circ$. A ray of light bounces from point $D$ on $BC$ to $E$ on $CA$ to $F$ on $AB$ and then back to $D$. Find the angles of $\triangle DEF$.

(Light always takes the shortest path between points, meaning it bounces off an edge at equal angles.)