复习“圆”这一单元内容时,要抓住学习要点,这就是与圆相切.特别是运用切线的性质与判定、切线长定理、三角形内切圆,以及两圆的公切线等相关性质的证明或计算. 一、掌握切线的性质与判定要抓住“过切点时半径垂直切线”这个重点,它是论证许多有关相切问题的关键 When reviewing the content of the circle, we must grasp the key points of learning. This is tangent to the circle. In particular, we must use the nature and judgment of the tangent, the tangent length theorem, the triangle inscribed circle, and the common tangent of the two circles. Proof or calculation. I. Grasping the nature of the tangent and the decision to grasp the key point of the “vertical tangent to the radius of the tangent point”, it is the key to the demonstration of many tangential problems.