Question

已知等比数列｛an}中a1加a2等于40,a3加a4等于160求a5+a6

Answer 1

设公比为q

a1+a2=40

a3+a4=a1*q^2+a2*q^2=(a1+a2)*q^2=160

则q^2=4

a5+a6=a3*q^2+a4*q^2=(a3+a4)*q^2=160*4=640