Question

等差数列中有S3／S6=1／3,则s6／s7=?

Answer 1

由题知3S3=S6

3[(a1+a3)*(3/2)]=(a1+a6)*(6/2)

3[(2a1+2d)*(3/2)]=(2a1+5d)*(6/2)

a1=2d

S6/S7=[(a1+a6)*(6/2)]/[(a1+a7)*(7/2)]

=[(2d+2d+5d)*3]/[(2d+2d+6d)*(7/2)]

=(27d)/(35d)

=27/35