.数列{an﹜是等差数列,且a3=3a〉0,数列﹛bn﹜满足b=an×an+1×an+1×an+2﹙n属于N*）且数列{bn﹜的前n项和为sn 则使得sn取最大值的n项是

题目

.数列{an﹜是等差数列,且a3=3a〉0,数列﹛bn﹜满足b=an×an+1×an+1×an+2﹙n属于N*）且数列{bn﹜的前n项和为sn 则使得sn取最大值的n项是
抱歉 试题错了 bn=an×an+1×an+2

答案

bn=(an+1)^2+1
sn=n+(a1+1)^2+(a2+1)^2+...+(an+1)^2
(an+1)^2>=0,当然是n越大sn越大.是题目有问题还是我哪里理解错了?