Question

等比数列｛a｝,若a1+a2+a3+a4=15/8,a2*a3=-9/8,则1/a1+1/a2+1/a3+1/a4=?

Answer 1

a1*a4=a2*a3=-9/8

1/a1+1/a2+1/a3+1/a4=(a1+a4)/(a1*a4)+(a2+a3)/(a2*a3)=(a1+a2+a3+a4)/(a2*a3)=(15/8)/(-9/8)=-5/3