[SOLVED] Help with proving a quadrilateral is a parallelogram. Hi this is my first post here and I'm glad to see that this is a well visited board. I'm having trouble with this one proof though that I have to do for geometry due tomorrow. Only a few other people I know have been assigned this specific one but they haven't done it yet. Given: A quadrilateral with a pair of congruent and parallel opposite sides. Prove: The quadrilateral is a parallelogram I know that I need to get the other two sides of the quad to be parallel, but I have no idea how to do that. I'm assuming first you have to make another construction, like connecting the opposite sides forming two triangles. I'd need to prove those triangles are congruent, but I can't because of the limited information given. So can someone try and help? PS: Why can't I attach Geometer's Sketchpad files to the post?