在涉及多个圆的问题中,引进根轴,并利用根轴的性质是十分有效的。因此,根轴是研究圆与圆位置关系的桥梁。1.圆幂过定点P的直线与定圆O交于A、B两点,则称PA·PB为点P对圆O的幂。由相交弦定理及切割线定理知,点P对圆O的 Among the problems involving multiple circles, it is very effective to introduce the root axis and make use of the properties of the root axis. Therefore, the root axis is to study the relationship between the location of the circle and the bridge. 1. A power over a fixed point P of the line and the fixed circle O to A, B two points, then PA · PB for the point P to the power of the circle O. By the intersection of chord theorem and cutting line theorem know, point P on the circle O