题目内容
（本题满分6分）先化简，再求值：
，其中
.
解：原式= 
· 
····················1分
= · 
························2分
=
······························4分
当=
﹣1时，原式= = 
= 
·············6分解析:
略
· 
····················1分=
· 
························2分=
······························4分当
=
﹣1时，原式= = 
= 
·············6分解析:略
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