In the paper conservation laws of a special form for systems of first-order differential equations depending on two dependent and independent variables are looked at. It is shown how the conservation laws can be used to solve hyperbolic-type and elliptic-type systems of equations that are come across in the theory of plasticity. Examples of an effective use of the described technique are given. With the use of the conservation laws was found the elastoplastic boundary in a problem of stress-strain state of a plate with free-form holes.