Geometry Problem 1339: Circle, Diameter, Tangent, Secant, Parallelogram. Math Infographic.
As shown in the figure below, EA is tangent to a circle of center O with
diameter AB at A and ECD is a secant. BC and BD cut EO at F and G,
respectively. Prove that AFBG is a a parallelogram. This entry contributed by Peter Tran.