解
见图
a2+a5=a2+a2q^3=9/8a3a4=a2q*a2q^2=1/8即：a2(1+q^3)=9/8(a2)^2*q^3=1/8解得：q^3=8,或q^3=1/8∵0∴q=1/2a2=1a1=a2/q=2an=a1(1-q^n)/(1-q)=2×(1-1/2^n)/(1-1/2)=4-2^(2-n)
a2*a5=a3*a4=1/8a5所以a2=1 a5=1/8,q=1/2a1=2an=2^(1-n)
