相似三角形的知识应用十分广泛,可证两直线平行、线段相等、线段比值、等积式,可求出线段的长、函数关系式等.本文逐一举例,说明其应用.一、证两直线平行例1如图,AB为半圆直径,O为圆心,AB=6,延长BA到F,使FA=AB.如果P为线段AF上的一动点(P与A不重合),PC切半圆于C,CD⊥AB于D,BE⊥PC于 The knowledge of similar triangles is widely used, which can prove that the two lines are parallel, the line segments are equal, the line segment ratio, the isosceles, the relationship between the length and the function of the line segment can be obtained. Example 1 As shown in the figure, AB is the diameter of the semicircle, O is the center of the circle, AB = 6, BA is extended to make FA = AB. If P is a moving point on line AF (P does not coincide with A) , CD ⊥ AB in D, BE ⊥ PC in