设{an}是各项互不相等的正数等差数列,{bn}是各项互不相等的正数等比数列,a1=b1,a2n+1=b2n+1,则(
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设{an}是各项互不相等的正数等差数列,{bn}是各项互不相等的正数等比数列,a1=b1,a2n+1=b2n+1,则( )
A. an+1>bn+1
B. an+1≥bn+1
C. an+1<bn+1
D. an+1=bn+1
A. an+1>bn+1
B. an+1≥bn+1
C. an+1<bn+1
D. an+1=bn+1
因为等差数列{an}和等比数列{bn}各项都是正数,且a1=b1,a2n+1=b2n+1,
所以an+1-bn+1=
a1+a2n+1
2-
b1•b2n+1=
a1+a2n+1−2
a1+a2n+1
2=
(
a1−
a2n+1)2
2≥0.
即 an+1≥bn+1.
故选 A.
所以an+1-bn+1=
a1+a2n+1
2-
b1•b2n+1=
a1+a2n+1−2
a1+a2n+1
2=
(
a1−
a2n+1)2
2≥0.
即 an+1≥bn+1.
故选 A.
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