(2011•郑州三模)数列{an}中,a3=2,a7=1,若{1an+1}为等差数列,则a11=( ) A.0 B.12 C.23 D.2
问题描述:
(2011•郑州三模)数列{an}中,a3=2,a7=1,若{
}为等差数列,则a11=( )1
an+1
A. 0
B.
1 2
C.
2 3
D. 2
答
设数列 {
}的公差为d1
an+1
∵数列{an}中,a3=2,a7=1,数列{
}是等差数列1
an+1
∴
=1
a7+1
+4d1
a3+1
将a3=2,a7=1代入得:d=
1 24
∵
=1
a11+1
+4d1
a7+1
∴a11=
1 2
故选B.