等差数列an中若公差d=2,a1+a4+a7＋……＋a28＝48,则,a3＋a6＋a9＋……＋a30等于

题目

等差数列an中若公差d=2,a1+a4+a7＋……＋a28＝48,则,a3＋a6＋a9＋……＋a30等于

答案

a3+a6+a9+...+a30
=(a1+2d)+(a4+2d)+(a7+2d)+...+(a28+2d)
=(a1+a4+a7+...+a28)+10×(2d)
=48+10×2×2
=48+40
=88