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# Sequences and series watch

1. Humm.. i'm having a few problems with this question set as part of homework.

Page 119 of P1 heinemann modular mathematics for edexcel AS and A level textbook. Question 20.

The first and last terms of an arithmetic series are -12 and 22. The sum of all the terms is 260. Find the number of terms in the series.

Could I have some pointers as to how to go about solving this?

Thanks,
James
2. Arggh, nvm. just sorted it out myself, I'm just having one of those days...

Sn = n/2 (a + L)

260 = n/2 (-12 + 22)

260 = n/2 x 10

520 = n x 10

n = 520/10 = 52

Humm, sorry about that. I'll think before I post next time

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