贵刊1986年第1期所登《浅谈平面几何论证中思维受阻的原因与对策》中的例2.(1)小题是一道以偏概全的命题。为叙述方便起见,现抄录于下: 例1.已知:△ABC的三条高交于H,CH=AB,BF=5cm。求证:∠ACB=45°错误分析:作者根据题意画出了图一,其实还遗漏了∠ACB是钝角的情况,即图二,由图二易证 The example of “The Reasons and Countermeasures for the Obstacles of Thinking in Plane Geometry Argument” published in the first issue of the Journal of You (1986) published in the Journal of You (1986) is a proposition that is partial in nature. For the sake of narrative convenience, it is reproduced below: Example 1. Known: Three highs of △ABC intersect at H, CH=AB, BF=5cm. Proof: ∠ ACB = 45 ° error analysis: The author according to the question intended to draw a map, in fact, also missing the ∠ ACB is an obtuse angle, that Figure II, from Figure 2 easy to prove