版主请删贴，谢谢

grass83 · 发表于 18-12-2014 01:16 AM

本帖最后由 grass83 于 23-10-2016 09:50 PM 编辑

版主请删贴，谢谢

showergel · 发表于 14-1-2015 12:30 AM

You need to understand how to derive the formula first.
From wikipedia

Just change (1-r) to (r-1) you will get the other Sn.

Foreign textbook only have one formula, which is

for all r not equal to 1. No matter r is +ve or -ve also the same equation.

conclusion: SPM 多左旧鱼

grass83 · 发表于 14-1-2015 02:07 AM

showergel 发表于 14-1-2015 12:30 AM
You need to understand how to derive the formula first.
From wikipedia

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