In basic mathematics we are taught the concept of the number line.This line extends horizontally from minus infinity on the left to plus infinity on the right with 0 being the center.
Any point on this line represents what is called a real number.The sum, difference, product or quotient of any two real numbers is also a real number.
However, there are some special numbers which are not represented on this line.These are called imaginary numbers.
The imaginary numbers can be thought of as existing on another line perpendicular to the real number line.
The first integer on this imaginary number line is denoted by the symbol i, which represents the square root of -1(In electrical engineering math, the symbol j is used instead as i usually is the symbol for current).
The sum of an imaginary number and real number gives us a class of numbers called complex numbers.
These are numbers which lie anywhere on the plane defined by these two number lines.
They are usually written as (a + bi) or alternately, they can be represented by a length and phase angle which are the distance and angle of the point from the intersection of the two number lines.
There are various rules which govern how to perform basic operations on complex numbers.
Complex numbers and imaginary numbers are used extensively in problems involving alternating current circuits.