a²-2a-3=0
(a-3)(a+1)=0
a=3或a=-1(舍去,分母为0,分式无意义）
[3/(a+1)-a+1]÷[(a²-4a+4)/(a+1)]
=[3/(a+1)-(a-1)]÷[(a-2)²/(a+1)]
=[3/(a+1)-(a²-1)/(a+1)]÷[(a-2)²/(a+1)]
=[(3-a²+1)/(a+1)]÷[(a-2)²/(a+1)]
=[(4-a²)/(a+1)]*(a+1)/(a-2)²
=(4-a²)/(a-2)²
=-(a²-4)/(a-2)²
=-(a-2)(a+2)/(a-2)²
=-(a+2)
=-a-2
=-3-2
=-5