The fourth type of special segment is the perpendicular bisector. It is a line or segment that passes through the midpoint of a side of a triangle and is perpendicular to that side. How many perpendicular bisectors can a triangle have?

The point of concurrency of the three perpendicular bisectors of a triangle is called the circumcenter. Notice that each point on the perpendicular bisector is the same distance from the ends of the segment it bisects. Since the circumcenter is on all three bisectors, it is equally distant from all three vertices of the triangle. Now a circle can be formed with the circumcenter as the center and the circle passing through each vertex. This circle is said to be circumscribed about the triangle.