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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

S_{n} = n/2 (a_{1} + a_{n}) 360 = n/2(42 - 26) 360 = 8n n = 45

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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