會考都無C
2020-9-21 22:39:13
唔算離地啦,普通sum of AS嚟
不過就咁問完又無application,唔似公開試風格
著拖鞋紅衫短袖
2020-9-21 22:39:46
Textbook
:^(
今日學AS
K85666
2020-9-21 22:45:23
Denote a as the 1st term, d as the common difference, Kn as the general term.
Kn = (n/2)(2a + (n-1)d)
= an + (nd/2)(n-1)
= (d/2)n^2 + (a-(d/2))n
After that the result can be obtained trivially by inputting the correct values for a and d.
Also one can use this result to obtain a and d from Kn for multiple choice questions.
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