yanahv7的部落格

標題:

maths 高手請答~

發問:

1. In an arithmetic sequence, T (4) + T(8) + T(12) + T(16) =224 Find the sum od the first 19 terms of this sequence. 列明steps plz~ ans is 1064

最佳解答:

Let the nth term of the arithmetic sequence be T(n) = a1 + (n - 1)d where a1 = 1st term, d = common difference T(4) + T(8) + T(12) + T(16) =224 [a1 + (4 - 1)d] + [a1 + (8 - 1)d] + [a1 + (12 - 1)d] + [a1 + (16 - 1)d] = 224 (a1 + 3d) + (a1 + 7d) + (a1 + 11d) + (a1 + 15d) = 224 4a1 + 36d = 224 a1 + 9d = 56 ................(1) The value of an arithmetic series (sum) consiting of n terms a1, a2, ... , anis given by the formula: Sn = a1 + a2 + ... + an = n[2a1 + (n -1)d] /2 sum of the first 19 terms of this sequence = S19 = a1 + a2 + ... + a19 = (19)[2a1 + (19 -1)d] /2 = (19)[2a1 + 18d] /2 = (19)(a1 + 9d) ...............................But from (1), a1 + 9d = 56 = (19)(56) = 1064

• 飛輪海寫真「海角一樂園」
• 中國旅行社 幾點關門~-
• Gauss-Jordan Elimination, 唔明白
• 李蘊入行經歷
• 我想切部電腦大約5000左右(唔包顯示屏)

此文章來自奇摩知識+如有不便請留言告知

其他解答:63D0B758E2D502CC