The perpendicular lines of the three sides of a triangle intersect at a point, which is called the outer center of the triangle, that is, the center of the outer circle of the triangle. The outer center of the triangle is equal to the distance between the three vertices of the triangle.
The intersection bisector of three internal angles of a triangle intersects at a point, which is called the center of the triangle, that is, the center of the inscribed circle of the triangle. The distance from the center of the triangle to the three sides of the triangle is equal.
The three center lines of a triangle intersect at a point, which is called the center of gravity of the triangle. The distance from the center of gravity of a triangle to the midpoint of each side is equal to one third of the center line of that side.
The three heights of a triangle intersect at a point, which is called the vertical center of the triangle.