Oh, I thought Figure 2 was the picture of the first question. My answer to the first question just now should be moved to the second question.

Now answer the first question. Extend AO to e in the opposite direction. Let AOC= angle 1, BOC= angle 2, BOD= angle 3 and DOE = angle 4. As can be seen from the figure, angle BOE= 90°, because angle COB+= angle 2+ angle 3 = 90, and angle BOE = angle 3+ angle 4 = 90.

It's complicated to write, so you should be able to understand it.

(2), ∠AOB and ∠COD are right angles, so ∠ AOB+∠ COD = 180, and the four angles are in the same plane, so the number of the remaining two angles ∠AOD and ∠COB = 360.