In mathematics, imaginary numbers are numbers in the form of a+b*i, where a and b are real numbers, b≠0, and i =- 1. The word imaginary number was founded by Descartes, a famous mathematician in the17th century, because the concept at that time thought it was a non-existent real number. Later, it was found that the real part A of the imaginary number a+b*i can correspond to the horizontal axis and the imaginary part B can correspond to the vertical axis on the plane, so that the imaginary number a+b*i can correspond to the points (a, b) on the plane.

The imaginary number bi can be added to the real number A to form a complex number in the form of a+bi, where the real numbers A and B are called the real part and imaginary part of the complex number respectively. Some authors use the term pure imaginary number to represent the so-called imaginary number, which refers to any complex number whose imaginary part is not zero.

To trace the trajectory of imaginary number, it is necessary to contact the emergence process of real number relative to it. We know that real number corresponds to imaginary number, which includes rational number and irrational number, that is, it is real number.