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有理数运算中,常发生以下几方面错误:一、概念不清例1 a和-a各是什么数?错解a是正数,-a是负数剖析:由于同学们初次学习正负数和错误的思维定势,误认为a是正数,-a是负数.正解:当a大于零时,a是正数,-a是负数;当a小于零时,a是负数,-a是正数;当a=0时,a和-a都是零.例2 已知|a-b|+a-b=0,比较a、b的大小.错解∵|a-b|=-(a-b)∴a-b<0,即a
In rational number operations, the following aspects often occur: First, the concept of unclear cases 1 What is the number of a and -a? A solution is a positive number, -a is a negative analysis: Because the students first learn positive and negative numbers and wrong Fixed mindset, mistakenly believe that a is a positive number, -a is a negative number. Positive solution: When a is greater than zero, a is a positive number, -a is a negative number; when a is less than zero, a is a negative number, -a is a positive number; when a = At 0, both a and -a are zero. Example 2 Known |ab|+ab=0, compares the sizes of a and b. 错|ab|=-(ab)∴ab<0, that is, a