1/(a+1)-[(a+3)/(a^2-1)]*[(a^2-2a+1)/(a^2+4a+3)]=1/(a+1)-[(a+3)(a-1)^2]/[(a+1)^2(a-1)(a+3)]=1/(a+1)-(a-1)/(a+1)^2=(a+1)/(a+1)^2-(a-1)/(a+1)^2=[(a+1)-(a-1)]/(a+1)^2=2/(a+1)^2又a^2+2a-1=0a^2+2a+1=2(a+1)^...