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smc

geometry senior

Problem

Quadrilateral is inscribed in circle and has side lengths , and . Let and be points on such that and . Let be the intersection of line and the line through parallel to . Let be the intersection of line and the line through parallel to . Let be the point on circle other than that lies on line . What is ?
(A)
(B)
(C)
(D)
Solution
Using the given ratios, note that By AA Similarity, with a ratio of and with a ratio of , so . Now we find the length of . Because the quadrilateral is cyclic, we can simply use the Law of Cosines. By Power of a Point, . Thus
Final answer
A