Angle Bisector

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.