形心坐標=(xA+xB+xC3,yA+yB+yC3) \text{形心坐標} = \left( \frac{x_A + x_B + x_C}{3}, \frac{y_A + y_B + y_C}{3} \right) 形心坐標=(3xA+xB+xC,3yA+yB+yC)