等差数列1,5,9……前10项和是

分类: 作业答案 • 2023-01-14 10:48:42

问题描述：

等差数列1,5,9……前10项和是

答

a1 =1 d=4
a10 = 1+ 4x9 = 37
s10 = ( 1+37) x10 /2 = 38 x5 = 190