Question

设an是等比数列,则下列数列,是等比数列的是?

Answer 1

ana(n+1)=a1^2q^(2n-1)=a1^2q (q^2)^(n-1)

an+a(n+1)=a1q^(n-1)(1+q)

an-a(n-1)=a1q^(n-1)(1-q)

1/an=1/a1 (1/q)^(n-1)

an+3=a1q^(n-1)+3

1,2,3,4都是等比数列,5不是.