设⊙Ｏ1,⊙Ｏ2 的半径分别为ｒ1,ｒ2 且ｒ2 ｒ1.可用以下两种简捷方法来求两圆的公切线方程 .方法 1　 1 )作出两圆的公切线与两圆连心线Ｏ1Ｏ2 的交点Ｐ ,求出点Ｐ分有向线段Ｏ1Ｏ2 的比λ =- ｒ1ｒ2(外公切线 )或λ =ｒ1ｒ2(内公切线 ) ;2 )由定比分点坐标公式求出点Ｐ的坐? Let ⊙O1 and ⊙O2 have radii of r1, r2 and r2 r1. The following two simple methods can be used to find the equations of the two circles’ common tangents. Method 1 1) Make two circles of public tangent lines and two circles of connecting lines O1O2 Intersection point P, find the ratio of point P to the directed line segment O1O2, λ =- r1r2 (tangent tangent) or λ = r1r2 (internal tangent); 2) Determine the point P’s siting by the point coordinate formula.