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Mathematics 17 Online
OpenStudy (anonymous):

find S20 for the series -1+(-3)+(-5) please explain how to do it

OpenStudy (anonymous):

20-1-3-5 o. o?

OpenStudy (anonymous):

no the 20th number in the series, sorry it should be -1+(-3)+(-5)...

geerky42 (geerky42):

So this sequence add up to 2 every time, start with one, so we have \(\Large S_n = -\sum_{k=1}^n ~ 2k-1 ~\longrightarrow ~-2\sum_{k=1}^n k +\sum_{k=1}^n1\)

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