You only really need to remember two rules when figureing out the angles of a triangle:
All angles add up to 180 inside a triangle
All angles on a line add up to 180, which is what doughboy showed which is how he got D and E inside the alpha and C triangles.
dkar i may suck at geometry but that IS DEFINITELY A TRIANGLE, NOT A TRAPEZIUM
He was doing the match by doing ABDE as a shape, instead of ignoring it. Unless i missed one, it looks like the triangle has 2 trapeziums in it.