First, explain the concept clearly, and then do more questions to understand it deeply, and compare it with the real function of high number. As for theorem proving, you can put it aside if you don't understand it. Give two examples, the relationship between differentiability of complex variable function f(z) and differentiability of two real functions and function analysis. The convergence interval of series 1-x 2+x 4- is (-1, 1), which can be answered without looking.