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HMMT November 2024 #0l25

HMMT November 2024Hard

From module Angle Chasing Mastery

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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.
TangentsTriangle trigonometryBrocard point, symmediansTrigonometryAngle chasing

Problem

Problem:

Let ABCABC be an acute triangle and DD be the foot of altitude from AA to BC‾\overline{BC}. Let XX and YY be points on the segment BC‾\overline{BC} such that ∠BAX=∠YAC\angle BAX = \angle YAC, BX=2BX = 2, XY=6XY = 6, and YC=3YC = 3. Given that AD=12AD = 12, compute BDBD.

Proposed by: Sarunyu Thongjarast

Answer: 122−16=288−1612 \sqrt{2} - 16 = \sqrt{288} - 16

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