Show that the coordinates $\left(x^{\prime}, y^{\prime}\right)$ and $\left(x^{\prime \prime}, y^{\prime \prime}\right)$ of the points of trisection of the segment with endpoints $\mathbf{S}\left(x_1, y_1\right)$ and $\mathbf{T}\left(x_2, y_2\right)$ are given by
$$
x^{\prime}=\frac{2 x_1+x_2}{3}, \quad y^{\prime}=\frac{2 y_1+y_2}{3}
$$
and
$$
x^{\prime \prime}=\frac{x_1+2 x_2}{3}, \quad y^{\prime \prime}=\frac{y_1+2 y_2}{3}
$$