Question

若等比数列{an}满足:a1+a2+a3+a4+a5=3,a1²+a2²+…a5²=12,

Answer 1

设原等比数列公比q,则所求的数列等比为-q

a1+a2+a3+a4+a5=3 a1(1-q^5)/(1-q)···A

,a1²+a2²+…a5²=12,a1^2(1-q^10)/(1-q^2)···B

a1-a2+a3-a4+a5=?a1(1=q^5)/(1+q)···C

B/A=C=4