Equations of motion of binary systems with variable masses

An equation is obtained for the relative motion of a binary system of variable mass. It is shown that the following equations can be obtained from it: the Gylden--Meshcherskii (G--M), Meshcherskii--Levi-Civita (M--L-C), and combined Gylden--Meshcherskii and Meshcherskii--Levi-Civita equations (G--M--L-C), which are used only for small time intervals. It is also shown that they do not have evolutionary significance for arbitrary laws of mass variation of the system