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贵刊93年第10期刊登的林俊同志的“巧用倒数知识解题”一文,读后颇受教益。该文例1、例2应用倒数知识解答确有独到之处,令人耳目一新。但笔者认为例3、例4若抓住“不变量”去进行解答,更符合学生的知识实际和心理承受能力,且算理浅显易懂,思路通畅清晰,步骤简捷明快。现把此两题解答如下:例3 有一个数,它的分母加1,可约简为1/2;分母减1,可约简为2/3,这个分数是()/()。分析:从题义可知,虽然由于这个分数的分母发生变化而引起自身的变化,但分子未发生变化,即分
Lin Jun published in the tenth issue of 93 published in Comrade Lin Jun “skillfully use the inverse knowledge to solve problems,” a text, read after teaching. The example 1, Example 2 using the inverse knowledge of the answer is indeed unique, refreshing. However, in my opinion, Example 3 and Example 4, if they seize “invariants ” to answer the questions, are more in line with the students' practical knowledge and psychological endurance, and they are easy to understand and understand. The ideas are clear and clear, and the steps are simple and neat. Now answer these two questions as follows: Example 3 has a number, which denominator plus 1, can be reduced to 1/2; denominator minus 1, can be reduced to 2/3, this score is () / (). Analysis: From the title we can see that, although due to changes in the denominator of this score caused its own change, but the molecule has not changed, that is, points