Online Geometry theorems, problems, solutions, and related topics.
See complete Problem 72Intersecting Circles, Cyclic Quadrilateral, Angles, Parallel. Level: High School, SAT Prep, College geometryPost your solutions or ideas in the comments.
ABCD is cyclic so angle BAD = angle DCF. Similarly DCFE is cyclic and angle DCF = 180 -angle FED. Hence AB is parallel to EF.
What about when BF intersects AE? that is another case, easy to proof, but is part of the problem.Greetings