The article considers third-order equations with multiple characteristics with general boundary value conditions and non-local initial data. A regular solution to the problem with known methods is constructed here. The uniqueness of the solution to the problem is proved by the method of energy integrals. This uses the theory of non-negative quadratic forms. The existence of a solution to the problem is proved by reducing the problem to Fredholm integral equations of the second kind. In this case, the method of Green’s function and potential is used.

We consider the second boundary value problem for nonstationary third-order equations of mixed type. and study asymptotic characteristics of fundamental solutions of the equations, which are used for constructing of regular solutions to the boundary value problems.

The paper is devoted to solutions of the third order pseudo-elliptic type equations. An energy estimates for solutions of the equations considering transformation’s character of the body form were established by using of an analog of the Saint-Venant principle. In consequence of this estimate, the uniqueness theorems were obtained for solutions of the first boundary value problem for third order equations in unlimited domains. The energy estimates are illustrated on two examples.

Рассматривается нелокальная краевая задача для нестационарного уравнения третьего порядка составного типа, в котором на границе области значения функции и их производные до второго порядка задаются в виде линейной комбинации, а начальные условия - в нелокальном виде. Доказывается однозначная разрешимость этой задачи. При доказательстве единственности решения задачи использованы метод интегралов энергии и теория квадратичных форм. При построении решения задач использованы теория потенциалов и интегральные уравнения Вольтерра. Изучены некоторые асимптотические свойства фундаментальных решений уравнения.