The concept of real axis and imaginary axis is complex number field. Complex number z=x+iy, where x is called the real part and y is called the imaginary part. Then the whole complex field is composed of points formed by coordinates (x, y). In the coordinate plane, the X axis is called the real axis and the Y axis is called the imaginary axis.

As shown in the following figure: line segment A 1A2 is called the real axis of hyperbola, and line segment B 1B2 is called the imaginary axis of hyperbola.

Extended data

Establish a rectangular coordinate system to represent the complex plane. The x axis is called the real axis, and the y axis is called the imaginary axis except the origin. The origin represents real number 0, and the origin is not on the imaginary axis. Every point on the complex plane has a unique complex number corresponding to it, and conversely, every complex number has a unique point corresponding to it, so the complex set C is one-to-one corresponding to the set of all points on the complex plane.

The complex plane is sometimes called Algonplane because it is used in Algongraph. They are named after Jean-Robert Algon1768-1822, although they were first described by Caspar Wessel, a Norwegian-Danish land surveyor and mathematician (1745-1818). Algongraph is often used to represent the positions of poles and zeros of a function on a complex plane.

If the square of a number is negative, then the number is imaginary; All imaginary numbers are complex numbers. The term "imaginary number" was invented by Descartes, a famous mathematician in17th century. Because of the concept at that time, it was considered to be a real number that did not exist. Later, it was found that the imaginary number can correspond to the vertical axis on the plane, and it is as real as the real number on the horizontal axis on the corresponding plane. The plane formed by the imaginary axis and the real axis is called the complex plane, and each point on the complex plane corresponds to a complex number.