Complex number
A complex number is represented by algebraic notation as
z = a + bi
The set of complex numbers is denoted by the symbol C.
Explanation
A complex number corresponds with a point in the complex plane. It consists of the real numbers a and b, and is written as
z = a + bi
The a is a real number and bi is an imaginary number. It can normally be used in calculations.
Every real numbers is also a complex number, because x = x + 0i. Also i itself is a complex number, because i = 0 + 1i. The real numbers are then a = 0 and b = 1. The imaginary unit i has only an imaginary part, and has therefore no real value.
Complex plane
The complex plane is a geometric representation of complex numbers, and consists of a real x-axis and orthogonaly the imaginary y-axis.