(4)
We see that equations (1), (2) and (3) involve independent and/or dependent variable
(variables) only but equation (4) involves variables as well as derivative of the dependent
variable y with respect to the independent variable x Such an equation is called a
differential equation In general, an equation involving  derivative (derivatives) of the dependent variable
with respect to independent variable (variables) is called a differential equation A differential equation involving derivatives of the dependent variable with respect
to only one independent variable is called an ordinary differential equation, e