ntions+for+section+9.4

If a tengent and secant (or a chord) intersect on a circle at the point of tangency, then the measure of the angle formed is **half** the measure of its intercepted arc.

The measure of an angle formed by two secants or chords that intersect in the interior of the circle is **half** the **sum** of the measures of the arcs intercepted by the angle and it's vertical angle x1+x2/2.

The measure of an angle formed by two secants that inersect in the exterior of a circle is **half** the **differences** of the measures of the intercepted arcs.

The measure of a tangent-tangent angle with it's vertex outside the circle is **x1-x2/2.**

The measure of a secant-tangent angle with its vertex outside the circle is **x1-x2/2**