1, imaginary unit I, whose square is equal to-1, that is, i2=- 1.

2. Pure imaginary number When a=0 and b0, the complex number a+bi is bi.

3. The real part and imaginary part of the complex number A+ A Bi are called the real part of the complex number, and B is called the imaginary part (note that both A and B are real numbers).

4. The sizes of two complex numbers cannot be compared, and we can only judge whether they are equal or unequal by definition.

5. The mathematical transformation between real space and virtual space is called Fourier transform, which is widely used in physics, electronics, number theory, combinatorial mathematics, signal processing, probability theory, statistics, cryptography, acoustics, optics, oceanography, structural dynamics and other fields, such as sine wave, square wave and sawtooth wave. Fourier transform uses sine waves as signal components.