切线是直线和圆的位置关系的重要内容.切线的判定和性质是学习其他圆的有关知识的基础.也是证明圆内一些基本问题的主要依据,学好切线的判定和性质,是顺利学习圆的知识的 The tangent is an important part of the relationship between the straight line and the circle. The judgment and nature of the tangent are the basis for learning the knowledge of other circles. It is also the main basis for proving some basic problems in the circle. Learning the nature and nature of the tangent is a matter of learning the circle smoothly. knowledgeable