阅读计算过程:
解:原式= ①
= ②
= ③
=
回答下列问题:
(1)步骤①错在______________________________;
(2)步骤①到步骤②错在______________________________;
(3)步骤②到步骤③错在______________________________;
(4)此题的正确结果是____________________。
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