等差数列{an}由2k项(k∈N*且k≥2),则S偶-S奇=kd还是kd/2?

问题描述:

等差数列{an}由2k项(k∈N*且k≥2),则S偶-S奇=kd还是kd/2?

S偶-S奇=kd,a2-a1=d,a4-a3=d,...,a2k-a(2k-1)=d