An angle bisector is a line or ray that divides an angle into two congruent angles.

In the figure, the ray bisects the angle .

Note that any point on the angle bisector is equidistant from the two sides of the angle. Some textbooks call this **Angle Bisector Theorem**, but this name is usually used for another theorem about angle bisectors in a triangle.

**Example :**

Since is an angle bisector,

Therefore,

By the Angle Addition Postulate,

Substitute.