AB is the diameter, so the angles AMB and ANB are right angles.
ANFE and MBFE are two rectangles.
Finally, EC*ED=EA*EM=FN*FB=FD*FC.
Get EC=DF.
2
ACB right triangle, AC*BC is twice the area of the triangle.
Passing c is high, and H * 2oc = AC * bc = oc 2.
Get h=OC/2.
Observe that the hypotenuse of the triangle CHO (drawn by yourself) is OC, which is twice as high as H, so the angle COH=30 degrees.
So CBA=30/2= 15.
Cab =75