A1+A4=18,→A1(1+q^3)=18....................(1) A2+A3=12,→A1q(1+q)=12.....................(2) (1)÷(2):(1+q^3)/q(1+q)=3/2→(1+q)(1-q+q^2)/q(1+q)=3/2→ (1-q+q^2)/q=3/2→2-2q+2q^2=3q→2q^2-5q+2=0→ (2q-1)(q-2)=0公比q为整数→q=2代入(1):A1(1+8)=18,A1=2 ∴S8=2(1-2^8)/(1-2)=510
a1+a4=18,a2+a3=12 a1+a1q^3=18, a1q+a1q^2=12 两式相比 (1+q^3)/(q+q^2)=3/2 (q^2-q+1)/q=3/2 2q^2-5q+2=0,公比为整数,q=2 a1+8a1=18, a1=2 S8=2(2^8-1)/(2-1)=2*255=510
A1+A4=A1(1+q^3)=18 A2+A3=A1(q+q^2)=12 (1+q^3)/(q+q^2)=3/2 (1-q+q^2)/q=3/2 q=2或q=1/2(舍去，公比为整数） S8=A1+A2+A3+A4+A1*q^4+A2*q^4+A3*q^4+A4*q^4 =(A1+A2+A3+A4)(1+q^4) =(18+12)(1+2^4)=510
答：a1+a2=18--->a(1+q=)18......(1) a3+a4=12--->aq^2(1+q)=12......(2) (2)/(1):q^2=2/3...详情>>
