已知各项不为零的等差数列{an}满足2a3-a72+2a11=0,数列{bn}是等比数列,且b7=a7,则b5b9=______.
问题描述:
已知各项不为零的等差数列{an}满足2a3-a72+2a11=0,数列{bn}是等比数列,且b7=a7,则b5b9=______.
答
∵2a3-a72+2a11=0,∴a72=2(a11+a3)
由等差数列的性质可得a72=2(a11+a3)=4a7,
解得a7=4,或a7=0
∵等差数列{an}的各项不为零,
∴a7=4,∴b7=a7=4,
由等比数列的性质可得16
故答案为:16
答案解析:由等差数列的性质可得a72=2(a11+a3)=4a7,结合题意可得b7=a7=4,再由等比数列的性质可得b5b9=b72,代值计算可得.
考试点:等差数列的性质.
知识点:本题考查等差数列和等比数列的性质,属中档题.