Concurrent Lines:
Concurrent lines are lines that intersect in one point.

Theorem:
The bisectors of angles of a triangle intersect at a point that is equidistant from the three sides of the triangle.

Theorem:
The perpendicular bisectors of the sides of a triangle intersect at a point that is equidistant from the three vertices of the triangle.

Theorem:
The lines that contain the altitudes of a triangle intersect at one point.

Theorem:
The medians of a triangle intersect at a point that is two thirds the distance from a vertex to the midpoint of the side opposite the vertex.