Lines L_{1}, L_{2}, and L_{3} are parallel
(Figure below) with OQ perpendicular to L_{2} (O on L_{3} and Q
on L_{2}). Circles O and Q with radius OQ intersect at A and B. AC
is tangent to circle O at A (C on L_{1}). DE is the perpendicular
bisector of OC (E on L2). Prove that triangle COE is
equilateral.
