I = incenter (intersections of 3 angle bisectors)[br]G = centroid (intersections of 3 medians)[br]O = circumcenter (intersections of 3 perpendicular bisectors)[br]H = orthocenter (intersections of 3 altitudes)[br]I is the center of incircle (inscribed circle of a triangle)[br]O is the center of circumcircle (triangle inscribed in a circle)[br]G, O, H are co-linear.