This paper mainly applies the basic properties of the circle, combined with the knowledge of similarity, Pythagorean theorem, acute angle trigonometric function and so on. This question is easy for candidates to lose points, which is also the difficulty of this question, so it is necessary to master the core methods and skills.

It is generally necessary to prove the leading angle. In fact, the relationship between tangency and parallelism is 90 degrees, and the relationship between lead angles is also used to judge parallelism. This kind of problem is usually solved by using the common auxiliary lines of the circle.

In order to skillfully solve geometric problems, we must form conditioned reflex to make auxiliary lines and solve problems. When you see a condition, a figure or a question in a question, you will immediately present possible auxiliary lines in your mind. So we must master the axioms and inferences we have learned skillfully.