在等比数列{an}中,A1+An=66,A2xAn-1=128,且其前几项和Sn=126,求n及公比q

A2*An-1=A1*An=128A1+An=66=>A1,An为方程xx-66x+128=0两根=>A1,An=2,64或64,2若A1=2,An=64=>q^(n-1)=32Sn=A1(1-q^n)/(1-q)=2*(1-32q)/1-q=126=>q=2,n=6若A1=64,An=2=>q^(n-1)=1/32Sn=A1(1-q^n)/(1-q)=64*(1-1/32q)/1...