Question

定義:F(x,y)=yx(x>0,y>0),已知數(shù)列{an}滿(mǎn)足:an=(n∈N*),若對(duì)任意正整數(shù)n,都有an≥ak(k∈N*)成立,則ak的值為(　　)

(A)(B)2(C)3(D)4

 

Answer 1

A

【解析】an=,==,2n2-(n+1)2=n2-2n-1,只有當(dāng)n=1,2時(shí),2n2<(n+1)2,當(dāng)n≥3時(shí),2n2>(n+1)2,即當(dāng)n≥3時(shí),an+1>an,故數(shù)列{an}中的最小項(xiàng)是a1,a2,a3中的較小者,a1=2,a2=1,a3=,故ak的值為.