Question

已知数列{a_n}既是等差数列又是等比数列，则这个数列的前n项和为

A.n                       B.na₁                      C.a₁ⁿ                            D.0

Answer 1

解析:由{a_n}既是等差数列又是等比数列,可知a_n=a₁≠0.∴S_n=na₁.

答案:B