等差数列中有S3/S6=1/3,则s6/s7=?

问题描述:

等差数列中有S3/S6=1/3,则s6/s7=?

由题知3S3=S63[(a1+a3)*(3/2)]=(a1+a6)*(6/2)3[(2a1+2d)*(3/2)]=(2a1+5d)*(6/2)a1=2dS6/S7=[(a1+a6)*(6/2)]/[(a1+a7)*(7/2)]=[(2d+2d+5d)*3]/[(2d+2d+6d)*(7/2)]=(27d)/(35d)=27/35