题目内容
(10分) 先化简，再求值：
，其中
．
当时，原式
解析:
解：原式
··········································· 2分
··························································· 4分
···················································································· 8分
当时，原式······························································· 10分
时，原式解析:解：原式
··········································· 2分··························································· 4分···················································································· 8分当
时，原式······························································· 10分 
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