Join the USAMO Guide Discord Server. Regular updates are posted there!

Let me Join!
Dismiss

HMMT Spring 2021 Guts Round #0kkn

HMMT Spring 2021 Guts RoundHard

From module Angle Chasing Mastery

Community difficultyNo ratings yetBe the first to rate this problem.
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.
TangentsAngle chasingTrigonometry

Problem

Problem:

A semicircle with radius 20212021 has diameter ABAB and center OO. Points CC and DD lie on the semicircle such that ∠AOC<∠AOD=90∘\angle AOC < \angle AOD = 90^\circ. A circle of radius rr is inscribed in the sector bounded by OAOA and OCOC and is tangent to the semicircle at EE. If CD=CECD = CE, compute ⌊r⌋\lfloor r \rfloor.

← Back to all problems