#### notes

We are already familiar with the equations of the type:

`x_2` – 3x + 3 = 0 ... (1)

sin x + cos x = 0 ... (2)

x + y = 7 ... (3)

Let us consider the equation:

x`(dy)/(dx)` + y = 0 ... (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.g.,differential equation.

2`(d^2y)/(dx^2) + ((dy)/(dx))^3` = 0 is an ordinary differential equation

.... (5)