圆是初中数学的重点内容之一,包括圆的有关性质、直线和圆的位置关系、圆和圆的位置关系以及正多边形和圆.其重点是:圆周角定理、垂径定理、切线的性质和判定定理、切线长定理及圆中的有关计算问题. The circle is one of the key contents of junior high school mathematics, including the nature of the circle, the positional relationship between the line and the circle, the positional relationship between the circle and the circle, and the regular polygons and circles. The emphasis is on the theorem of the circle angle, the vertical theorem, and the nature of the tangent. And determination theorem, tangent length theorem and related calculation problems in circles.