∠ ACB = 90 (the circumferential angle of the diameter is a right angle)
∠CBA=90 -25 =65
2. Do OM⊥AB in M, and extend the intersection of OM in N to connect OB.
Then ob = r = 2cm, on = r = 2cm, Mn = om = 1cm (because Mn and om coincide).
According to Pythagorean theorem, BM=√3 cm is obtained.
According to the vertical diameter theorem, AB=2√3 cm is obtained.