You will need

- Protractor, ruler.

Instruction

1

Let the known length of the chord AB and the angle AOB between the

**radii**conducted to the ends of the chord. We find these data the radius of the circle with center at point O.2

Triangle AOB is isosceles because OA = OB = R. By a property of an isosceles triangle the height of the OE is a median and a bisector of the angle AOB. Denote the angle AOB for x

Triangle AEO is rectangular with right angle AEO. Since the height TH is also the bisector of the angle AOB, the angle AOE = x/2. Then from the right triangle AOE, we have: OA = R = (AB/2)/sin(x/2).

Triangle AEO is rectangular with right angle AEO. Since the height TH is also the bisector of the angle AOB, the angle AOE = x/2. Then from the right triangle AOE, we have: OA = R = (AB/2)/sin(x/2).