Direct introduction method: Direct introduction method is direct guidance method. We are used to "cut to the chase" when talking and writing articles, so that the theme is prominent and the argument is clear. When some newly taught mathematical knowledge is difficult to attract people with the help of old knowledge, we can directly point out the topic and immediately arouse students' interest in learning. For example, when teaching sine and cosine in trigonometric functions, you can introduce it like this; What is the ratio of the opposite side to the hypotenuse and the ratio of the adjacent side to the hypotenuse of acute angle A in a right triangle? In this lesson, we will learn these contents-sine and cosine. This import is very simple. It not only clarifies the theme of this class, but also explains the background of this class.