Abstract functions are generally in the form of y=f(x), which can't be expressed by numbers and letters. They usually appear in topics, and may have definition fields, value fields and so on. 1 Abstract function is often combined with periodic function, such as: f(x)=-f(x+2) f(x)=f(x+4) 2 to solve abstract function problems, assignment method is usually adopted, and the classical problem of F(0) F( 1) abstract function is often solved first in college entrance examination mathematics. ! ! We call a function that does not give a specific analytical expression an abstract function. Because this kind of questions can comprehensively examine students' understanding of the concept and nature of functions, and abstract function questions combine the definition range, range, monotonicity, parity, periodicity and images of functions, they appear constantly in the college entrance examination; For example, the 2002 Shanghai College Entrance Examination 12 questions, the 2004 Jiangsu College Entrance Examination 22 questions, and the 2004 Zhejiang College Entrance Examination 12 questions. When students solve such problems, they often feel that they have no way to start and the correct rate is low. This paper talks about some superficial views on the solution of such problems. 1. Special value method: It has unexpected effects when dealing with multiple-choice questions. Example 1 the function f(x) defined on r satisfies f (x+y) = f (x)+f (y )(x, y∈R), when x