问题描述: 等比数列an中,有a3*a11=4a7,数列bn是等差数列,且b7=a7,则b5+b9= 1个回答 分类:综合 2014-11-24 问题解答: 我来补答 a3·a11=4a7a1q^2*a1q^10=4a1q^6a1^2q^12=4a1q^6a1q^6=4=a7=b7b5+b9=b1+4+b1+8d=2b1+12d=2(b1+6d)=2b7=2*4=8 展开全文阅读