# Difference between revisions of "2012 USAJMO Problems"

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===Problem 4=== | ===Problem 4=== | ||

− | Let <math>\alpha</math> be an irrational number with <math>0 < \alpha < 1</math>, and draw a circle in the plane whose circumference has length 1. Given any integer <math>n \ge 3</math>, define a sequence of points <math>P_1</math>, <math>P_2</math>, <math>\dots</math>, <math>P_n</math> as follows. First select any point <math>P_1</math> on the circle, and for <math>2 \le k \le n</math> define <math>P_k</math> as the point on the circle for which the length of arc <math>P_{k - 1} P_k</math> is <math>\alpha</math>, when travelling counterclockwise around the circle from <math>P_{k - 1}</math> to <math>P_k</math>. | + | Let <math>\alpha</math> be an irrational number with <math>0 < \alpha < 1</math>, and draw a circle in the plane whose circumference has length 1. Given any integer <math>n \ge 3</math>, define a sequence of points <math>P_1</math>, <math>P_2</math>, <math>\dots</math>, <math>P_n</math> as follows. First select any point <math>P_1</math> on the circle, and for <math>2 \le k \le n</math> define <math>P_k</math> as the point on the circle for which the length of arc <math>P_{k - 1} P_k</math> is <math>\alpha</math>, when travelling counterclockwise around the circle from <math>P_{k - 1}</math> to <math>P_k</math>. Suppose that <math>P_a</math> and <math>P_b</math> are the nearest adjacent points on either side of <math>P_n</math>. Prove that <math>a + b \le n</math>. |

[[2012 USAJMO Problems/Problem 4|Solution]] | [[2012 USAJMO Problems/Problem 4|Solution]] | ||

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===Problem 5=== | ===Problem 5=== | ||

## Revision as of 16:06, 13 April 2014

## Contents

## Day 1

### Problem 1

Given a triangle , let and be points on segments and , respectively, such that . Let and be distinct points on segment such that lies between and , , and . Prove that , , , are concyclic (in other words, these four points lie on a circle).

### Problem 2

Find all integers such that among any positive real numbers , , , with there exist three that are the side lengths of an acute triangle.

### Problem 3

Let , , be positive real numbers. Prove that

## Day 2

### Problem 4

Let be an irrational number with , and draw a circle in the plane whose circumference has length 1. Given any integer , define a sequence of points , , , as follows. First select any point on the circle, and for define as the point on the circle for which the length of arc is , when travelling counterclockwise around the circle from to . Suppose that and are the nearest adjacent points on either side of . Prove that .

### Problem 5

For distinct positive integers , , define to be the number of integers with such that the remainder when divided by 2012 is greater than that of divided by 2012. Let be the minimum value of , where and range over all pairs of distinct positive integers less than 2012. Determine .

### Problem 6

Let be a point in the plane of triangle , and a line passing through . Let , , be the points where the reflections of lines , , with respect to intersect lines , , , respectively. Prove that , , are collinear.

Solution The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.