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Geometry Difficulty 5.3 AIME, harder Find the answer

G3 The vertices AA and BB of an equilateral ABC\triangle A B C lie on a circle kk of radius 1 , and the vertex CC is inside kk. The point DBD \neq B lies on k,AD=ABk, A D=A B and the line DCD C intersects kk for the second time in point EE. Find the length of the segment CEC E.

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

## Solution

As AD=AC,CDAA D=A C, \triangle C D A is isosceles. If A D C= A C D=\text{A D C= A C D=} and B C E=\text{B C E=}, then β=120α\beta=120^{\circ}-\alpha. The quadrilateral ABEDA B E D is cyclic, so A B E=180 -\text{A B E=180 -}. Then C B E=\text{C B E=} 120α120^{\circ}-\alpha so C B E=\text{C B E=}. Thus CBE\triangle C B E is isosceles, so AEA E is the perpendicular bisector of BCB C, so it bisects B A C\text{B A C}. Now the arc BEB E is intercepted by a 3030^{\circ} inscribed angle, so it measures 6060^{\circ}. Then BEB E equals the radius of kk, namely 1 . Hence CE=BE=1C E=B E=1.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.