一个与切割线有关的图形性质:如图1,过圆O外一点P作圆的两条切线PA,PB和一条割线PCD,连接AC,AD,BC,BD,则ACAD=BCBD.图1图2我们将它记作性质1.很明显,△PAC∽△PDA,△PBC∽△PDB,则ACAD=PAPD=PBPD=BCBD,即ACAD=BCBD.这是一个简单漂亮的性质,有着很广泛的应用,数学竞赛中有很多平 A graphical relationship with the cutting line: As shown in Figure 1, the circle O outside a point P for the circle two tangent PA, PB and a secant PCD, connecting AC, AD, BC, BD, then ACAD = BCBD Figure 1 Figure 2 We will refer to it as property 1. Obviously, △ PAC∽ △ PDA, ΔPBC∽ △ PDB, then ACAD = PAPD = PBPD = BCBD, that is, ACAD = BCBD. This is a simple and beautiful nature, The application of mathematics competition has many levels