Question

等差数列{a}中,an不等于0,2a3+a7^2+2a11=0,数列{b}是等比数列,且b7=a7,则b6b8=?

Answer 1

解;根据等差数列的性质有a3+a11=2a7 则2a3+a7^2+2a11=0即4a7+a7^2=0 则a7=-4

则b7=a7=-4

再根据等比数列的性质

b6*b8=b7^2=16