Online Geometry Problem 798: Parallelogram, Secant Line, Tangent Circles, Circumcircles,
Triangle. Level: High School,
SAT Prep, College,
Mathematics Education

The figure below shows a parallelogram ABCD,
a secant line meets DA extended, AB, BC, and DC extended at E, F, G, and
H, respectively. Prove that the circumcircles of triangles EDH and GCH
are tangent at H.