题目内容
（本小题满分7分）先化简，再求值：
，其中
.
解：原式
········································ （2分）
····························································· （2分）
······························································································ （2分）
当时，原式的值为1。 （ 1分）解析:
略
········································ （2分）····························································· （2分）······························································································ （2分）当
时，原式的值为1。 （ 1分）解析:略
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