Question

{an}为等差数列,{bn}为等比数列,且b1=a1^2,b2=a2^2,b3=a3^2

Answer 1

题目欠完整

设公差为d>0,由{bn}为等比数列得

a2^4=a1^2a3^2,

∴a2^2=土a1a3,即（a1+d)^2=土a1(a1+2d),

d^2=0(舍）,2a1^2+4a1d+d^2=0,

d=(-2土√2）a1,

a2=a1+d=(-1土√2）a1,

{bn}的公比q=(a2/a1)^2=3干2√2,

由lim （b1+b2+···+bn）=√2+1知|q|