先化简,再求值:a-1/a+2·a平方-4/a平方-2a+1除以1/a平方-1,其中a满足a平方-a-7=0
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[(a-1)/(a+2)]×[(a²-4)/(a²-2a+1)]÷[1/(a²-1)]
=(a-1)(a²-4)(a²-1)/[(a+2)(a²-2a+1)]
=(a-1)(a+2)(a-2)(a+1)(a-1)/[(a+2)(a-1)²]
=(a-2)(a+1)
=a²-a-2
=(a²-a-7)+5
=0+5
=5
=(a-1)(a²-4)(a²-1)/[(a+2)(a²-2a+1)]
=(a-1)(a+2)(a-2)(a+1)(a-1)/[(a+2)(a-1)²]
=(a-2)(a+1)
=a²-a-2
=(a²-a-7)+5
=0+5
=5
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