1.1-2+3-4+...-50+51=?
2.(5×2)+(5×4)+(5×6)+...+(5×998)
如何計算以下算式????????最好有埋公式?
2020-07-19 9:26 am
回答 (1)
2020-07-19 1:49 pm
✔ 最佳答案
1)1-2 + 3-4 +...+ 49-50 + 51
=(-1 + -1 + ...+ -1 ) + 51
∵ 1,3, ... ,49 的數目共有 : (1+49)/2 = 25個
∴ 1-2 + 3-4 +...+ 49-50 + 51
= -25 + 51
= 26
2)
(5×2)+(5×4)+(5×6)+...+(5×998)
= 5 (2+4+6+....+998)
= 5(2) (1+2+3+...+499)
= 10 (499/2) (1+499) ---→ { n項之和=n(a+L)/2 }
= 1,247,500
收錄日期: 2021-04-18 18:34:49
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20200719012649AAtpULK