The explanation of middle school is limited to independent variables and dependent variables. Many students always think that functions should have consistent expressions, and they don't even understand piecewise functions. They think that two functions are spliced together. Only by transforming the university into a generalized mapping concept can we fully understand it.

2。 Limit.

It gives people a wrong impression that it is a dynamic process that can be realized, causing many misunderstandings. In fact, it is not a process, and the limit symbol is an assignment operation symbol. The process can't reach the limit. Lim symbol means to take an unattainable value, so it is called "taking the limit".

3。 An angle exceeding 360 degrees.

Beyond the intuition of life, some people can't even recognize the angle over 180 degrees.