PERPENDICULAR BISECTORS / CIRCUMCENTER
These are the PERPENDICULAR BISECTORS.
Their point of concurrency is the CIRCUMCENTER.
Notice that the CIRCUMCENTER is equidistant to the VERTICES.
Drag the vertices of the triangle around, and notice that the CIRCUMCENTER is ALWAYS equidistant to the VERTICES.
Make an acute triangle, a right triangle, and an obtuse triangle. Notice where the CIRCUMCENER is in each case.