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Find S_10 for -1+-7+-13+-19+... Arithmitic Sequences for Algebra 2, thank you

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basede | eNotes Newbie

Posted July 18, 2013 at 2:33 AM via web

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Find S_10 for -1+-7+-13+-19+... Arithmitic Sequences for Algebra 2, thank you

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aruv | High School Teacher | (Level 2) Valedictorian

Posted July 18, 2013 at 2:45 AM (Answer #1)

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Given sequence is in arithmetic series  its first term is a= -1 and commn differnce is d= (-7+1)=-6

Sum of n terms of an AP wth a frst term and comn difference d s

`S_n=(n/2)(2a+(n-1)d)`

Thus

`S_10=(10/2)(2(-1)+(10-1)(-6))`

`=5(-2-54)`

`=5(-56)`

`=-280`

Ans.

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