They have a radius O radius. A is a point outside the circle. From point A, draw a line through the circle B and another line through the circle M and across the diameter O of the circle. It is known that AB = 20cm and AM = 10cm. Calculate the radius R of the circle O. They have a radius O radius. A is a point outside the circle. From point A, draw a line through the circle B and another line through the circle M and across the diameter O of the circle. It is known that AB = 20cm and AM = 10cm. Calculate the radius R of the circle O.