在排列、组合应用题的教学中,学生解题容易犯重复或遗漏的错误,而且由于情况复杂数字又大,所以不易检查错在哪里。下面介绍两种具体的验算和纠错的方法。 1 写出所有的排列或组合来检验,当元素较多时可适当缩小元素的个数来检验。例1 从1,2,3,4,7,9这六个数中,任取出两个 In the teaching of arranging and combining application problems, students often find it difficult to duplicate or omit mistakes in solving problems, and because the situation is complicated and the numbers are large, it is not easy to check where they are wrong. Two specific methods for checking and correcting errors are described below. 1 Write out all permutations or combinations to test. When there are many elements, check the number of elements appropriately. Example 1 Take two of the six numbers 1, 2, 3, 4, 7, and 9