计算题 a-1分之1减1-a的2次方分之2

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1/（a-1）-2/(a^2-1)
=(a+1)/(a-1)(a+1)-2/(a^2-1)
=(a+1-2)/(a-1)(a+1)
=(a-1)/(a-1)(a+1)
=1/(a+1)