解
(a-2)/(a²-1)÷[1-(2a-3)/(a-1)]
=(a-2)/(a-1)(a+1)÷[(a-1)/(a-1)-(2a-3)/(a-1)]
=(a-2)/(a-1)(a+1)÷(2-a)/(a-1)
=-(2-a)/(a-1)(a+1)×(a-1)/(2-a)
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