HMMT February 2019 Team Round #0k61

HMMT February 2019 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.

Roots of unityIntermediate Value TheoremComplex numbers

Problem

Problem: Prove that for all positive integers $n$ , all complex roots $r$ of the polynomial

P(x) = (2 n) x^{2 n} + (2 n-1) x^{2 n-1} + \cdots + (n+1) x^{n+1} + n x^{n} + (n+1) x^{n-1} + \cdots + (2 n-1) x + 2 n

lie on the unit circle (i.e. $|r|=1$ ).

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