等差數,第4項係3,公差係5 ,搵列數的公項
公式 A+(n-1)D
無首項甘點做??
更新1:
重有一題 5.8.11.14,尾項係95 ,搵個總項數
中5數,等差數
回答 (2)
2007-09-13 2:10 am
✔ 最佳答案
首先找出公項T(4) = A + (4 - 1)(5)
3 = A + 3(5)
A = -12
首項是 - 12
公項
= - 12 + (n - 1)(5)
= 5n - 17
2007-09-21 19:06:08 補充：
首項，a = 5公差，d = 8 - 5 = 3所以，5 (n - 1)(3) = 953(n - 1) = 90n - 1 = 30n = 31所以，總項數為31
參考: Myself~~~
2007-09-13 2:11 am
首項係唔係咁呀?
A + (n-1)D = 3
A + (4-1)5 = 3
therefore A = -12
pleaes comment
A + (n-1)D = 3
A + (4-1)5 = 3
therefore A = -12
pleaes comment
收錄日期: 2021-04-21 13:56:57
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