2.已知{an}为等差数列,bn为等比数列,其公比q不等于1,且bi>0（i=1,2,3,4,5...）,若a1=b1,则（）A．a6=b6B.a6>b6C．a6b6或a6刚才漏了一个已知条件:a11=b11

Question

2.已知{an}为等差数列,bn为等比数列,其公比q不等于1,且bi>0（i=1,2,3,4,5...）,若a1=b1,则（ ）
A．a6=b6 B.a6>b6
C．a6b6或 a6
刚才漏了一个已知条件:a11=b11

Answer 1

with your added condition,B is the correct answer.a6=(a1+a11)/2,b6=sqrt(b1*b11),we know that (a+b)/2>=sqrt(ab),with the condition that b2/b1 is not 1,then the "=" does not apply.