=(c+d)-(a-b)=2+3=5

(2) The AOD angle is a right angle, that is, the AOD angle is 180 degrees.

The angle BOD= 180-50= 130 degrees.

α is the bisector of the angle BOD,

The angle COD= 130/2=65 degrees.

(3) Teachers can take student A for a distance, while student B walks to the museum. The teacher will let him go first (let him walk by himself) and pick up student B later. Finally, three people will arrive at the same time.

Suppose each student walks for x hours and rides a motorcycle for y hours. The student's arrival time is X+Y hours, and the teacher should also be X+Y hours. Minus the time for the teacher to drive the students, it takes X-Y hours for the teacher to return to pick up the students halfway. Recalculate the distance (now it is more appropriate to call it displacement): students walk 5X+20Y=33, teachers walk 20*2Y-25*(X-Y)=33, and simultaneously solve X= 1.8, Y= 1.2, and X+Y is exactly 3 hours.