The angle must measure 90º; that is, any triangle with a base that
is the diameter of a circle is a right triangle.
The distance from O to the left edge of the crescent has a
length of x - 9. In this figure, this segment is OY.
Using the two similar right triangles OYX and OXZ, this
proportion can be written:
Using x for ZO, .
for x gives a radius of 25 units for the larger circle. The two
diameters are 50 and 41 units.