大多几何问题,都需要适当添加辅助线,构造出平行、相似、全等、垂直等一些比较熟悉的图形,才能解决.例1已知如图1,直角梯形ABCD中,AD∥BC,AD⊥AB于A、BC⊥AB于B,AB=6,以AB为直径的⊙O和CD切于点E,求CE·DE的值.解连结OD、OC、OE.由题意可知,AD、BC是⊙O的切线.又CD切⊙O于E,∴ Most of the geometric problems need to be properly added to the auxiliary lines to construct parallel, similar, congruent, vertical, and other relatively familiar graphics to solve. Example 1 is known as Figure 1, right-angle trapezoid ABCD, AD ∥ BC, AD ⊥ AB in A, BC ⊥ AB in B, AB = 6, with AB as the diameter of the ⊙O and CD cut at point E, find the CE DE value. Solution OD, OC, OE. Known by the meaning of the question, AD, BC is the tangent line of ⊙O. Then CD cuts O to E, ∴