C refers to the set of complex numbers in mathematics, and the number in the form of z = A+bi(A and B are both real numbers) is called a complex number, where A is called the real part, B is called the imaginary part, and I is called the imaginary part. When the imaginary part of z is equal to zero, z is often called a real number.

Complex number set contains real number set, so it is an extension of real number set. Complex number was first put forward by Cardan, a scholar in Milan, Italy, in the16th century. Through the work of D'Alembert, De Moivre, Euler and Gauss, this concept was gradually accepted by mathematicians.