题目内容
（5分）先化简，再求值：
，其中a＝－2，b＝
．
，其中a＝－2，b＝．解：原式
········································· 2分
····················································································· 3分
································································································ 
4分
当a=－2，b=1时，原式=
= 
························································· 5分
········································· 2分····················································································· 3分································································································ 4分当a=－2，b=1时，原式=
= ························································· 5分略
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