1/n^2-n +1/n^2+n)/ n+3/n^2-1

1/n(n-1)+1/n(n+1)=(n+1+n-1)/[n(n²-1)]=(2n/[n(n²-1)]=2/(n²-1) 2/(n²-1)8* (n²-1)/(n+3)=2/(n+3)