课堂上，学完等比定理后，张老师在黑板上写了如下题目：例1若上，求k的值．要求会做的同学板演．李小刚毫不犹豫地举起了手，要求板演，他是这样做的：解由等比定理得写完后，得意洋洋地回到座位上．张老师看后说：“李小刚，你又粗心了．同学们，你们知道他错在哪里吗？”同? In the classroom, after completing the equal-ratio theorem, Teacher Zhang wrote the following questions on the blackboard: Example 1 If on, find the value of k. Asked to do classmates play. Li Xiaogang raised his hand without hesitation and asked for a performance. He did this: After the solution was written by the equal theorem, he happily returned to his seat. After reading, Zhang said: “Li Xiaogang, you are careless again. Students, do you know where he is wrong?” Same?