First of all, it is necessary to prove that am = MD. Because ∠O is a right angle, do you think that the straight line AM=MD=MO is a right angle △AOD? All right. It is now proved that AM = MOMD = MO is as follows

First prove AM=MO: that is, prove ∠ Mao =∠AOM, and find the condition. We know that ∠CAD=∠DBC, ∠DBC=∠COM (because △CHO is similar to △COB, and H is the intersection of OM and BC, which is the vertical foot). So COM=∠CAD=CAM. So AM=MO.

Then prove that MD=MO:

That is to say, it proves that ∠MOD=∠MDO. Similarly, because ODM=OCB=MOD, (△OHB is similar to △COB), it is proved that.