High school. Exponential function is high school knowledge. Junior high school students learn linear function, proportional function, inverse proportional function, quadratic function and simple trigonometric function. High school function is to learn exponential function, logarithmic function and power function on the basis of junior high school function. Exponential function is a basic elementary function in high school mathematics, and it is also the key and difficult point of high school mathematics. Examination questions often appear in college entrance examination. Exponential function is generally the content in the first volume of senior high school mathematics (compulsory) published by People's Education Press and Jiangsu Education Press.