**Interior angle formed by 2 chords=1/2 the sum of the intercepted angle

**Exterior angle formed by 2 secants=1/2 the difference of the intercepted arcs

**Exterior angle formed by a secant and a tangent=1/2 the difference of the intercepted angle

**Angle formed by a tangent and secant to the point of tangency=1/2 the intercepted arc

**Exterior angle formed by 2 tangents=1/2 the difference of the intercepted arcs