S2n=(2n)^2-1/4S(2n-2)=(2n-2)^2-1/耐液4a2n=S2n-S(2n-2)=8n-4=4*(2n-1)a(2n-2)=4*(2n-3)a2n-a(2n-2)=8所以是等差数列1/Sn=1/(n^2-1/4)=1/(n-1/2)-1/(n+1/2)代入即可得{1/备做Sn}的前n项昌滚物和为1-1/(n+1/2)