设公比是qa1+a2=a1(1+q)=3a3+a4=a1(1+q)*q^2=6所以q^2=2a7+a8=a1(1+q)*q^6=a1(1+q)*(q^2)^3=3*2^3=3*8=24
a3+a4=(a1+a2)q^2q^2=(a3+a4)/(a1+a2)=6/3=2a5+a6=(a3+a4)q^2=6*2=12
