圆的切线是圆这一章的重点内容之一,它的判定定理、性质定理及其推论,是学习其他有关圆的知识的理论基础,是进行圆内线段相等、角相等、弦相等、弦平行、线段成比例的证明与计算的主要依据.因此,要想学好圆的知识,学好圆的切线是关键. The tangent of a circle is one of the key parts of the circle. Its decision theorems, property theorems, and inferences are the theoretical basis for learning other circle-related knowledge. They are equal in line, equal in angle, equal in chord, and in a circle. The main basis for the proof and calculation of the proportionality of the parallel and line segments. Therefore, if you want to learn the circular knowledge, it is the key to learn the round tangent.