0, 1, 2 are all fulcrums. Take the closed curves around 0, 1 and 2 respectively. Obviously, the radial angle increment near the three is 2π, so they are all fulcrums.

The concept of complex number originated from finding the roots of equations. When finding the roots of quadratic and cubic algebraic equations, the square root of negative numbers appeared. For a long time, people couldn't understand this figure. However, with the development of mathematics, the importance of such numbers is increasingly apparent.

The theory of complex variable function came into being in18th century. 1774, Euler considered two equations derived from the integration of complex variables in one of his papers. Before him, French mathematician D'Alembert had obtained them in his paper on fluid mechanics.

Characteristics of complex variable function:

The calculation of complex integral is slightly different from the second kind of curve integral. Compared with real variable function, the calculus theory of complex variable function has a more beautiful conclusion. If real change is the patch of calculus, then complex change is the perfect application of calculus itself.

The concepts of completeness and consistency of real numbers are the only slightly difficult points in fractions. These foundations are not discussed much in complex variables, but the difficulties of complex variables focus on complex geometry and multiple complex variables.