(a的平方+a-1/a+1)-(a的平方-3a+1/a-3)
=[(a²+a)-1]/(a+1)-[(a²-3a)+1]/(a-3)
=(a²+a)/(a+1)-1/(a+1)-(a²-3a)/(a-3)-1/(a-3)
=a-1/(a+1)-a-1/(a-3)
=-1/(a+1)-1/(a-3)
=[-(a-3)-(a+1)]/(a+1)(a-3)
=(2-2a)/(a²-2a-3)
(a的平方+a-1/a+1)-(a的平方-3a+1/a-3)
=[（a²+a-1)(a-3)-(a+1)(a²-3a+1)]/(a+1)(a-3)
=(a³+a²-a-3a²-3a+3-a³+3a²-a-a²+3a-1)/(a+1)(a-3)
=(-2a+2)/(a+1)(a-3)
原式=[(a²+a-1)(a-3)-(a²-3a+1)(a+1)]/(a+1)(a-3)
=(³-2a²-4a+3-a³+2a²+2a-1)/(a+1)(a-3)
=(-2a+2)/(a²-2a-3)
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