HMMT Spring 2021 Team Round #0knb

HMMT Spring 2021 Team RoundHard

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Understand the scale

Scale 0.5: Easiest math competition problems, often solvable even for early middle school students without experience. 1: Problems strictly for beginners, often at a moderate middle school level. 1.5: Problems for stronger beginner students, on the level of the middling problems in most middle school contests. 2: For motivated beginners, harder questions from the previous categories. 2.5: More advanced beginner problems, hardest questions from previous categories. 3: Early intermediate problems that require more creative thinking. 3.5: Tougher early intermediate problems that consistently stretch into higher-level creative thinking or conceptual knowledge. 4: Intermediate-level problems. 4.5: Upper intermediate problems approaching the upper bound for non-invitational sprint math competitions. 5: More difficult AIME problems or simple proof-based Olympiad-style problems. 6: High-level AIME-styled questions or introductory Olympiad-level questions. 7: Tougher Olympiad-level questions, may require more technical knowledge. 8: High-level Olympiad-level questions. 9: Expert Olympiad-level questions. 9.5: The hardest problems appearing on Olympiads which the strongest students could reasonably solve. 10: Historically notorious problems, generally unsuitable for even very hard competitions because they are exceedingly tedious, long, and difficult.

Problem

Problem:

Let scalene triangle $A B C$ have circumcenter $O$ and incenter $I$ . Its incircle $\omega$ is tangent to sides $B C, C A$ , and $A B$ at $D, E$ , and $F$ , respectively. Let $P$ be the foot of the altitude from $D$ to $E F$ , and let line $D P$ intersect $\omega$ again at $Q \neq D$ . The line $O I$ intersects the altitude from $A$ to $B C$ at $T$ . Given that $O I \parallel B C$ , show that $P Q = P T$ .