在学习立体几何时 ,免不了要画截面 ,判断截面形状 ,或者判断所截几何体形状 ,但有的同学往往从主观愿望出发 ,马马虎虎看一遍题目 ,就自以为弄清已知条件了 ,然后匆忙写出结果或过程 ,从而导致“一看就会 ,一做就错”的现象 ,试看以下两例 .1　截面是什么例 1　已知正三棱柱Ａ When studying solid geometry, you must inevitably draw sections, judge section shapes, or determine the shape of the cut geometry. However, some students often start from a subjective wish and look at the topic in a careless manner, thinking that they understand the known conditions, and then hurry to write. The result or process, which leads to the phenomenon of “when you look at it and you do it right”, see the following two examples. 1 What is the cross section? Example 1 Known trigonal prism A