There are two variables x and y in the process of change. If for each value of X, Y has a unique value corresponding to it, then X is an independent variable and Y is a function of X. ..

2. The concepts of linear function and proportional function.

If the relationship between two variables x and y can be expressed as y=kx+b(k, b is a constant, k≠0), then y is a linear function of x (x is an independent variable), especially when b=0, y is a proportional function of x.

Description:

(1) The range of independent variables of a linear function is all real numbers, but it should be determined according to the actual meaning of the function in practical problems.

(2) the linear function y=kx+b(k, b is a constant, b≠0) has the same meaning as the linear equation and linear inequality, that is, the degree of the independent variable x is 1, the linear coefficient k must be a non-zero constant, and b can be an arbitrary constant.

(3) When b=0 and k≠0, y=b is still a linear function.

(4) When b=0 and k=0, it is not a linear function.