A. N. Kusyumov
Department of Aerohydrodynamics
Kazan State Technical University
Karl Marks Str. 10, Kazan, 420111, Russia
The second order ordinary differential equations systems that generally cannot be obtain from the variational principle are considered. Each equation of that system can be presented as the sum of two expressions. The first expression follows from the variational principle. The second expression does not follow from the variational principle. Such system we shall call the quasi Euler - Lagrange system. Under a certain requirements to the Lie transformations group the quasi Euler - Lagrange system conservation laws can be obtained in explicit form (similarly to the Noether theorem).