I'm curious if it looks like I defined the reasons correctly to prove that FBCD is indeed a parallelogram. Specifically, I'm unsure if I'm using #4 "definition of coincident" and #5,6 "reflexive property" correctly in their terminology. I don't have anyone else, or any teacher to ping this back to or I would try to not waste space here. This is my finished proof: I apologize about cutting the top half of the worked problem off. It should be mirrored to the unworked problem above. If it helps, I can repost the image upon request.