first-order differential equation

is: a differential equation in which no derivative of the dependent variable of order higher than first order appears. [P5.4]

has: a general solution which always involves the introduction of an arbitrary constant. This constant can only be determined in any particular situation by imposing an appropriate boundary condition. [P5.4]

usually is assumed: to be of the first degree and may be written in the general form

[M6.2]