1+4+7+....+46
項數跟和?
拜託各位大大~
等差級數答案
2012-02-12 8:39 am
回答 (2)
2012-02-12 9:04 am
✔ 最佳答案
1 +4 + 7 ...... + 46第一項：T(1) = a = 1
公差： d = 4 - 1 = 7 - 4 = 3
T(n) :
a + (n - 1)d = 46
1 + (n - 1) x 3 = 46
3(n - 1) = 45
n - 1 = 15
n = 16
項數 = 16
和
= 1 + 4 + 7 ...... + 46
= n[T(1) + T(n)] / 2
= 16 x (1 + 46) / 2
= 376
參考: micatkie
2012-02-14 12:16 am
項數 : an= 46
= 1+(n-1)3
= 3n-2
3n=48
n= 16
n項的和 : S16
= 16x(46+1) / 2
= 8x47
= 376
= 1+(n-1)3
= 3n-2
3n=48
n= 16
n項的和 : S16
= 16x(46+1) / 2
= 8x47
= 376
收錄日期: 2021-04-13 18:31:40
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20120212000010KK00369