Function expression is to express a specific operation to be performed by a function with a specific algebraic expression, which clearly describes what kind of operation a function has to complete.

For example, elementary functions: quadratic function f(x)=a*x*x+b*x+c, trigonometric function sin(x), cos(x) and other power functions, exponential function, logarithmic function, trigonometric function, inverse trigonometric function, and constants undergo finite rational operations (addition, subtraction, multiplication, division, rational power, rational number power).

Functional data:

In the process of a change, the amount of change is called a variable (in mathematics, the variable is X, and Y changes with the change of X value), and some numerical values do not change with the variable, so they are called constants.

Independent variable (function): a variable related to other quantities, and any value in this quantity can find a corresponding fixed value in other quantities.

Dependent variable (function): it changes with the change of independent variable. When the independent variable takes a unique value, the dependent variable (function) has and only has a unique value corresponding to it.

Function value: in a function where y is x, x determines a value, and y determines a value accordingly. When x takes a, y is determined as b, and b is called the function value of a. ..