a6·a7·a8/(a1·a2·a3)=q^15=24/3=8 则q=2^(1/5)
a9·a10·a11/(a6·a7·a8)=q^9=2^(9/5)
故a9·a10·a11=24*2^(9/5)=48*2^(1/5)