Advanced proof of parallelograms having equal areas

SOLUTION FOUND. You can extend EF and CB until they intersect.
http://i900.photobucket.com/albums/ac204/lamp23/par.jpg

If all you are given is that ABCD and DEFG are parallelograms then you can't prove they have the same area- it's not true! It is not true that all parallelograms have the same area. What properties of ABCD and DEFG are you given that you haven't mentioned?

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Originally Posted by HallsofIvy

What properties of ABCD and DEFG are you given that you haven't mentioned?

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Well, the picture shows obviously that and .