教学中经常会遇到一些同学在解题中出现顾此失彼的思维现象 .下面摘录几例予以剖析 ,以引起同学们的关注 .一、概念不清例 1　如图 1 ,ABCD为矩形 ,E、F分别是OA、OD的中点 ,求证 :四边形BCFE为等腰梯形 .错证　∵ABCD为矩形 ,∴AD ∥BC ,且OA =OB=OC=OD .又E、F分别为OA、OD的 Often encountered in the teaching of some students in the solving problems appear to miss out on the phenomenon of thinking. The following excerpts of several cases to be analyzed in order to arouse the attention of the students. First, the concept is not clear examples 1 In Figure 1, ABCD is a rectangle, E, F They are the midpoints of OA and OD respectively. Prove that the quadrilateral BCFE is an isosceles trapezoid. The wrong certificate ∵ ABCD is rectangular, ∴ AD ∥ BC, and OA = OB = OC = OD. And E, F are OA, OD, respectively.