一、忽视“且”与“或”的不同含义例1 当x为何值时,分式x2-x/(x+2)(x-1)有意义错解:当分母等于零时,分式无意义由分母(x+2)(x-1)=0,得x=-2或1 所以,当x≠-2或x≠1时,分式有意义剖析:本题分式x2-x/(x+2)(x-1)无意义用“或”, 有意义用“且”.对“或”的关系的否定是“且”的关系. 正解:当x≠-2且x≠1时,分式有意义. 二、对分式值为零的条件掌握不牢 I. Disregarding the Different Meanings of “and” and “or” Example 1 Fractional x2-x/(x+2)(x-1) is meaningfully misinterpreted when the value of x is: when the denominator is equal to zero, the fraction is not The meaning of the denominator (x+2)(x-1)=0 is given by x=-2 or 1. Therefore, when x≠-2 or x≠1, the fractional meaningful analysis: The fraction of this question x2-x/( x+2)(x-1) meaningless use “or”, meaning use “and”. The negation of the relationship of “or” is the relationship of “and”. Positive solution: when x ≠ -2 and x ≠ 1 Fractional is meaningful. Second, the conditions for the fractional value of zero are not stable