求(r^4+r^2+1)/(r^4+r)的前n项和

就都用n来写吧由公式可知n^4+n^2+1=(n^6-1)/(n^2-1)=(n^3+1)(n^3-1)/(n^2-1)=(n^3+1)(n^2+n+1)/(n+1)n^4+n=n(n^3+1)故(n^4+n^2+1)/(n^4+n)=(n^2+n+1)/(n^2+n)=1+1/n(n+1)=1+ 1/n - 1/(n+1)所以其前n项和Sn=1+1/1-1/2...