已知等差数列{an}的公差d=-2,a1+a4+a7+.+a97=50,

问题描述:

已知等差数列{an}的公差d=-2,a1+a4+a7+.+a97=50,

题目不全

a3+a6+a9+...+a99
=a1+2d+a4+2d+a7+2d+...+a97+2d
=(a1+a4+…+a97)+(33*2)d
=(a1+a4+…+a97)+66d
=50-132
=-82