变形：(1^2-0)/2^2 -(2^2-1)/3^2 (3^2-2)/4^2 -(4^2-3)/5^2 (5^2-4)/6^2现在看明白了吧?下一项是-(6^2-5)/49=-31/49 通项公式：an=(-1)^(n+1)[n^2-(n-1)]/(n+1)^2=(-1)^(n+1)(n^2-n+1)/(n+1)^2