G3 The vertices A and B of an equilateral △ABC lie on a circle k of radius 1 , and the vertex C is inside k. The point D=B lies on k,AD=AB and the line DC intersects k for the second time in point E. Find the length of the segment CE.
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
## Solution
As AD=AC,△CDA is isosceles. If A D C= A C D= and B C E=, then β=120∘−α. The quadrilateral ABED is cyclic, so A B E=180 -. Then C B E=120∘−α so C B E=. Thus △CBE is isosceles, so AE is the perpendicular bisector of BC, so it bisects B A C. Now the arc BE is intercepted by a 30∘ inscribed angle, so it measures 60∘. Then BE equals the radius of k, namely 1 . Hence CE=BE=1.
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