The set of complex numbers, represented by the symbol C, is formed by all numbers that can be written in the form z=a+bi, where a and b are real numbers, and i is the imaginary unit. Here, a is called the real part and b is called the imaginary part of the complex number.
If b=0, the number is an imaginary number. Conversely, if b=0, the number is real. Both real numbers and imaginary numbers are subsets of the complex number set.