an = a1q^(n-1)a1,(1/2)a3,2a2成等差数列2a2+a1= a32a1q+a1=a1q^2q^2-2q-1=0q=1+√2(a9+a10)/(a7+a8)=a1q^8(1+q)/[a1a^7(1+q)]=q=1+√2
