Problem 344. Quadrilateral, Extension of sides, Circle, Tangent, Semiperimeter. Level: High School, College, SAT Prep.
The figure shows a quadrilateral ABCD.
The extension of the sides are tangent to circle O at E, F, G,
and H. If s is the semiperimeter of the quadrilateral, prove
that s = AB + BC = AD + CD.