1, the complex number was first put forward by Italian Milan scholar Cardin in16th century. Through the work of D'Alembert, De Moivre, Euler, Gauss and others, this concept is gradually accepted by mathematicians.

2. Generally, numbers in the form of z=a+bi (both a and b are real numbers) are called complex numbers. Where a is called the real part, b is called the imaginary part, and I is called the imaginary part. When the imaginary part b of z = 0, then z is a real number; When the imaginary part b≠0 and the real part a = 0 of z, z is often called pure imaginary number. Complex number field is an algebraic closure of real number field, that is, any polynomial with complex coefficients always has roots in complex number field.