两圆外切时,该切点和一条外公切线与两圆的两个切点构成的三角形称为“切点三角形”.如图1,⊙O1与⊙O2外切于点P,AB为⊙O1和⊙O2的外公切线,A、B为切点.则△APB为切点三角形,它有一个重要的性质,即∠APB=90°.为了证明这一性质,不妨过点P作⊙O1和⊙O2的内公切线PC,交AB于点C.因 When the two circles are circumscribed, the tangent point and the triangle formed by two tangents of the two tangents of the circle and the two circles are called “cutting point triangles.” As shown in Figure 1, ⊙O1 and ⊙O2 are circumscribed at point P, and AB is ⊙. The tangents of O1 and ⊙O2 are tangent points, and A and B are tangent points. Then ΔAPB is a cut-point triangle. It has an important property, that is, ∠APB=90°. To prove this property, you may wish to use point P for ⊙O1. And ⊙O2’s internal tangent PC, cross AB at point C.