Khan Academy Static

In this tutorial, we study lines that are perpendicular to the sides of a triangle and divide them in two (perpendicular bisectors). As we'll prove, they intersect at a unique point called the cicumcenter (which, quite amazingly, is equidistant to the vertices). We can then create a circle (circumcircle) centered at this point that goes through all the vertices. This tutorial is the extension of the core narrative of the Geometry "course". After this, you might want to look at the tutorial on angle bisectors.

3749_2003_AIME_II_problem_7.html

3746_Circumcenter_of_a_right_triangle.html

3745_Circumcenter_of_a_triangle.html

3748_Area_circumradius_formula_proof.html

3747_Three_points_defining_a_circle.html