(九年义务教育)人教版初三《几何》课本P129例4中,⊙O1、⊙O2外切于A,BC是⊙O1、⊙O2的外公切线,B、C是切点,求证:AB⊥AC.(如图1) 我们仔细看一下△ABC:它实际上是由两圆相外切的切点A,外公切线与两圆相切的切点B、C三个切点连线围成的.因此,把它称为 (Nine-year Compulsory Education) PEP Third Edition “Geometry” Textbook P129 Case 4, ⊙O1, ⊙O2 circumscribed in A, BC is 外O1, ⊙O2 grandfather tangent, B, C is a cut-point to verify: AB⊥AC. (Figure 1) Let’s take a closer look at △ABC: it is actually a tangent point A circumscribed by two circles, and three tangent points tangent points B and C tangent to the tangent of the grandfather to the two circles. Surrounded by. Therefore, call it