Theorem 9.1 (Centroid).
The three medians of the triangle with vertices \((x_i, y_i)\), \(i = 1, 2, 3\), meet at the
centroid
\[ \left ( \frac {x_1 + x_2 + x_3}{3}, \frac {y_1 + y_2 + y_3}{3} \right ), \]
which lies two-thirds of the way along each median from its vertex.