Question: why are the circumcenter orthocenter and centroid collinear?
Answer: Theorem 1 The orthocentre, centroid and circumcentre of any trian- gle are collinear. The centroid divides the distance from the orthocentre to the circumcentre in the ratio 2:1. The line on which these 3 points lie is called the Euler line of the triangle. to denote the circumcircle of the triangle ABC.