Line Through the Incircle Center of a Tangential Quadrilateral

Problem

A convex quadrilateral ABCDABCD is circumscribed about a circle OO; that is, each of its four sides is tangent to the circle. A line through OO meets the sides ABAB and CDCD at KK and LL, and meets the diagonals ACAC and BDBD at MM and NN, respectively. Suppose that BKL=CLK\angle BKL=\angle CLK, AM=1AM=1, MC=2MC=2, and BN=3BN=3.

figure

Find NDND.

Answer

Solution

Difficulty8/10
Topicsplane geometry, Law of Sines, Similar Triangles, Tangent Circle

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