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在正确答案唯一存在的选择题解法中,有如下一种不妥的叙述: 当选择支之间存在“包含”关系时,可将“被包含”的选择支淘汰掉。上述方法被称为“互相淘汰”法。其例为: 例1 若s:n~4a+cos~4a=1,则sina+cosa的值为 (A) 1; (B) -1 (C) 1或-1。解答案(A)、(B)包含于(C)、若(A)、(B)中至少有一个正确,则(C)必正确。这与正确答案的唯一性相矛盾。故淘汰(A)、(B),正确答案为(C)。笔者认为上述解法不妥。请看下例。例2 函数y=x~(1/2)的反函数的图象是抛物线
In the only solution to a multiple-choice problem where the correct answer exists, there is an inappropriate narrative as follows: When there is an “inclusive” relationship between the selected branches, the “contained” alternative can be eliminated. The above methods are called “mutual elimination”. Examples are: Example 1 If s:n~4a+cos~4a=1, the value of sina+cosa is (A) 1; (B) -1 (C) 1 or -1. If the answers (A) and (B) are contained in (C), and if at least one of (A) and (B) is correct, (C) must be correct. This contradicts the uniqueness of the correct answer. Therefore, (A) and (B) are eliminated. The correct answer is (C). The author believes that the above solution is not proper. Please see the following example. Example 2 The image of the inverse of the function y=x~(1/2) is a parabola