We found out how to figure out Gauss-Bonnet for spherical geometry in our class, which was using the sum from 1 to n of (alpha + beta + gamma) - pi and turning this into 2piX(x).
We are supposed to try to find Gauss-Bonnet for hyperbolic and Euclidean. I think I can get it for hyperbolic, it seems very similar to spherical. However, Euclidean he said to work backwards? I'm confused with this, it seems like it is trickier and I don't know where to start.