找規律題,1/4,-1/3,7/16,-13/25,7/12

找規律題,1/4,-1/3,7/16,-13/25,7/12

變形:(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現在看明白了吧?下一項是-(6^2-5)/49=-31/49通項公式:an=(-1)^(n+1)[n^2-(n-1)]/(n+1)^2=(-1)^(n+1)(n^2-n+1)/(n+1)^2