Another Way

I was just thinking of how the professor was talking about the angle 180 and 360 and thought of another proof which I think may work. Can someone verify it?

whoa....

@angeliccanary That would definitely work! You found that the three angles, 180a, 180b, and 180y must add to 360 degrees because they form a "full rotation." Actually, some people go the opposite way: they start with the fact that the angles in a triangle add to 180 degrees, and use that to actually prove that the exterior angles must add to 360 degrees... can you see how?

No offence but can you make the pic less messy so I can read it? I don't have good eyesight.