性质

等差数列

等比数列

1

若m + n = s + t，则a_m + a_n = a_s + a_t

若m + n = s + t，则a_m * a_n = a_s * a_t

2

m + n = 2K，则a_m + a_n = 2a_k

m + n = 2K，则a_m * a_n = a_k²

3

{a_n}中任意两项a_m，a_n都有a_n = a_m + (n − m)d

{a_n}中任意两项a_m，a_n都有a_n = a_m * q^{n− m}