Which angle is the greatest one? I admit that my question had a certain amount of malice and was overcome by the subtleness of Nina Guindilla's response...
The big fish eats the little fish but angles are not fish...
The exercise on angles was easy:
Nina Guindilla commented that it was very easy from the formulas for the angles outside and inside a circle.
alpha + beta = gamma/2 + delta/2 + gamma/2 – delta/2 = gamma
alpha – beta = gamma/2 + delta/2 – gamma/2 + delta/2 = delta