If A, B, C,… be the successive bending- moments involved, the equations to find them have the following characteristics : The first involves A and B only, the second A, B and C only, the third (if more than three) B, C and D only, and so on for all intermediate equations; finally, the last equation contains only the last two unknowns.

The method to be considered applies more generally, however, when each equation in succession contains only one additional unknown, so that the third may contain A, B, C and D, the fourth A, B,C, D and E, and so on.