有这样一道题：“计算：x2-2x+1x2-1÷x-1x2+x-x的值，其中x=2012．”甲同学把“x=2012”错抄成“x=2021”，但他的计算结果也是正确的．这是怎么回事？你能给予合理的解释吗？

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