Tennis Court

I was playing tennis this weekend and I realized that geometry included both the wall in the background and the net in the image below.

Each individual square is a parallelogram. With drawings on the Geometer's Sketchpad, I was able to prove theorems 5-1 to 5-8.

The measure of angle C is 106.66 degrees, angle D is 73.34 degrees, angle B is 106.66 degrees, and angle A is 73.34 degrees. Same side interior angles measured 180 degrees, and the total angle measure was 360 degrees. (~WM5)