例题如图1,⊙O1和⊙O2外切于点A,BC是⊙O1和⊙O2的外公切线,B、C为切点,求证:AB⊥AC.纵观近几年的中考试题,与此题相关的试题层出不穷.现举几例加以说明,以供参考.例1(2003年天津)已知,如图2,⊙O1与⊙O2外切于点A,BC是⊙O1和⊙O2的外公切线,B、C为切点.(1)求证:AB⊥AC;(2)若r1、r2分别为⊙O1和⊙O2的半径,且r=2r2,求AB/AC的值. In the example shown in Figure 1, ⊙O1 and ⊙O2 are circumscribed at point A, BC is the tangent of ⊙O1 and ⊙O2, B and C are tangent points, and verification: AB⊥AC. Throughout the examination questions in recent years, and The questions related to this topic are endless. Here are a few examples to illustrate for your reference. Example 1 (Tianjin, 2003) is known. As shown in Figure 2, ⊙O1 and ⊙O2 are circumscribed at point A, and BC is ⊙O1 and ⊙O2. The grandfather’s tangent, B, C is the cut point. (1) Proof: AB⊥AC; (2) If r1, r2 are the radius of ⊙O1 and ⊙O2, respectively, and r = 2r2, find the value of AB/AC.