n. a set of differential equations that are to be simultaneously satisfied. A set of simultaneous linear differential equations that occurs frequently (for example, in finding streamlines) is of the formwhere P, Q and R are functions of the three variables x, y, z. The solution of these equations is sought by transforming them to a total differential equation; the method is to find constants a, b, c such thathas either zero denominator and an exact numerator, or a numerator that is the differential of the denominator.