  The principle of finding an integrating factor for a none exact differential
equations is extended to a class of third order differential equations. If the
third order equation is not exact, under certain conditions, an integrating
factor exists which transforms it to an exact one. Hence, it can be reduced
into a second order differential equation. In this paper, we give explicit
forms for certain integrating factors of a class of the third order
differential equations.

Classical Analysis and ODEs