Homework Help: Arithmetic Series

Posted by Embraced on Tuesday, January 10, 2012 at 9:25pm.

Find n for the arithmetic series with Sn = 360, a1=42 and an= -26

Arithmetic Series - Steve, Wednesday, January 11, 2012 at 12:21am
S_n = n/2 (a₁ + a_n)
360 = n/2(42 - 26)
360 = 8n
n = 45
Arithmetic Series - Anonymous, Friday, January 13, 2012 at 10:54pm
May I ask how did you get that 8n...I'm having trouble working it out on paper for another problem

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