In a certain change process, there are two variables X and Y. If Y has a unique definite value for each definite value of X within a certain range, it corresponds to it according to certain corresponding rules, then Y is the function of X, X is called the independent variable, the range of X is called the domain of function, the value of Y corresponding to the value of X is called the function value, and the set of function values is called the range of value.

Exponential function: generally speaking, the function y = ax (a > 0, and a≠ 1) is called exponential function, where x is the independent variable. The domain of a function is r.

Logarithmic function is the inverse function of exponential function, and the textbook is based on the property that the images of two functions as inverse functions are symmetrical about the straight line y = X.

The function y = x a is called a power function, where x is an independent variable and a is a constant (only the case where a is a rational number n is discussed here).