Triangle Centers
source:
Math is Fun
www.geogebra.org/classic
(1)內心 incenter (角平分線 angle bisector)
(2)外心 circumcenter (中垂線 perpendicular bisector)
(3)重心/形心 centroid (中點 median / midpoint)
(4)垂心 orthocenter (垂直線 altitude)