For example we have line $A$ with coordinates $(0, 1, 10, 9)$;
And we need to divide this line by $3$ (so we have now $A_1, A_2$ and $A_3$), where $A_1 + A_2 + A_3 = A$; Is there equation, to find coordinates of $A_1, A_2$ and $A_3$ points?
With best regards