D
若{a n}是等差数列,
则a 1+a 2+…+a n=na 1+
d,
∴b n=a 1+
d=
n+a 1-
,
即{b n}为等差数列;若{c n}是等比数列,则c 1·c 2·…·c n=c 1 n·q 1 +2+…+(n-1)=c 1 n·q
,∴d n=
=c 1·q
,
即{d n}为等比数列,故选D.
D
若{a n}是等差数列,
则a 1+a 2+…+a n=na 1+
d,
∴b n=a 1+
d=
n+a 1-
,
即{b n}为等差数列;若{c n}是等比数列,则c 1·c 2·…·c n=c 1 n·q 1 +2+…+(n-1)=c 1 n·q
,∴d n=
=c 1·q
,
即{d n}为等比数列,故选D.