设数列 {an} 的前 n 项和为 Sn,则 {an} 等差。

(1) S n4=n 2+2n, n=1,2,3

(2) S n4=n 2+ 2n +1,n=1,2,3

A、条件(1)充分,但条件(2)不充分
B、条件(2)充分,但条件(1)不充分
C、条件(1)和(2)单独都不充分,但条件(1)和条件(2)联合起来充分
D、条件(1)充分,条件(2)也充分
E、条件(1)和(2)单独都不充分,但条件(1)和条件(2)联合起来也不充分
查看答案
正确答案:

A

答案解析:

等差数列的前n项和公式为Sn=An2+Bn,A、B为全体实数,因此条件(1)充分,条件(2)不充分,选A。

上一题
你可能感兴趣的试题

About 20 of the passengers who were injured in a plane crash are said to be in_____condition .

A、decisive
B、urgent
C、vita
D、critical

In1991,whilet11eeconomiesofindustrializedcountriesmetaneconomic_____,theeconomiesofdevelopingcountriesweregrowingveryfast.

A、reviva
B、repression
C、recession
D、recovery

After his uncle died ,the young man _____the beautiful estate with which he changed from a poor man to a wealthy noble .

A、inhabited
B、inherited
C、inhibited
D、inhaled

We aim to ensure that all candidates are treated fairly and that they have equal______to employment opportunities .

A、entrance
B、entry
C、access
D、admission

His wife has been _______a lot of pressure on him to change his job.

A、taking
B、exerting
C、giving
D、pushing
热门试题 更多>
相关题库更多>
英语
综合能力
试卷库
试题库