已知数列S n =n 2 -7n,∴a 1 =s 1 =-6,当 n≥2时,a n = 已知数列S n =n 2 -7n,∴a 1 =s 1 =-6,当 n≥2时,a n = 发布时间:2025-07-02 13:57:56