充分挖掘习题潜在的规律是同学们提高探究能力的一个途径.现对一道习题进行探讨.题目如图1,⊙O_1和⊙O_2外切于点A,BC是⊙O_1和⊙O_2的外公切线,B、C为切点,求证:AB⊥AC.思考1:探究命题的一题多证.证法1:如图1,过点A作⊙O_1和⊙O_2的内公切 Fully tap the potential law of exercises is a way for students to improve their ability to explore is now an exercise to explore the problem shown in Figure 1, ⊙ O_1 and ⊙ O_2 circumscribed at point A, BC is ⊙ O_1 and ⊙ O_2 of the male public tangent, B, C as the cut-off point, verify: AB ⊥ AC. Reflections 1: Exploring the subject of a question more evidence. Aspect 1: As shown in Figure 1, over point A for ⊙ O_1 and ⊙ O_2 of the public cut