解1：√(Sn)=√{1+1/(n^2)+1/[(n+1)^2]}√(Sn)={1/[n(n+1)]}√{(n^2)[(n+1)^2]+(n+1)^2+n^2}√(Sn)=[1/(n^2+n1)]√(n^4+2n^3+3n^2+2n+1)
