In this problem, an angle like angle BAC where the
vertices like on the circle itself is called the inscribed angle.
While angle BOC, where O is the center of the circle, is
called the central angle.
Using Proposition III.20 from Euclid's Elements, this is called
the Inscribed Angle Theorem wherein:
∠BOC = 2∠BAC
or ∠BOC / 2 = ∠BAC
