A. N. Kusyumov
Department of Aerohydrodynamics
Kazan State Technical University
Karl Marks Str. 10, Kazan, 420111, Russia
The system of exterior equations appropriate to an arbitrary partial differential equations set (with parameter) of the first order is considered. The concept of "cut"-transformation and the concept of "restore"-transformation, defined by the action of some transformations group, are entered. The restore-transformation allows determining "noninvariant" symmetries of partial differential equations set. The noninvariant symmetries are used for construction of the exact and approximate solutions of the initial equations set.