(a-1)/[(a+1)^2-4]=(a-1)/[(a+3)(a-1)]=1/(a+3)=2(a-1)/[2(a-1)(a+3)] (1-a)/(2-4a+2a^2)=(1-a)/[2(a-1)^2]=-1/[2(a-1)]=-(a+3)/[2(a-1)(a+3)]