Draw a ray from the vertex of an angle and divide it into two equal angles. This ray is called the bisector of an angle. The intersection of bisectors of three angles of a triangle is called the center of the triangle.

Properties of angular bisector

1. The distance from a point on the bisector of an angle to both sides of the angle is equal.

2. The points from the inside of the corner to both sides of the corner are on the bisector of the corner. (reverse application)

The line segment from the vertex of a triangle to the intersection of its internal angle bisector is called the bisector of the triangle.

The bisector of a triangle is not the bisector of an angle: one is a line segment and the other is a ray.

The bisector of triangle angle has an interesting property: the bisector of angle A in triangle ABC is AD, then AB:AC=BD:CD. (Can be proved by area method)

The three bisectors of a triangle intersect at a point, which is the center of the triangle, and the distances from the center to the three sides are equal.