Final answer:
The angle between tangents and the radius of a circle determines the length of OP.
Step-by-step explanation:
The angle between two tangents drawn from an external point P to a circle of radius a and center O depends on the position of P with respect to the circle.
If the angle is 90∘, then OP=2a.
If the angle is 60∘, then OP=a.
If the angle is 120∘, then OP=3a.
If the angle is 180∘, then OP=[infinity].