October 15th, 2011, 07:57 AM  #1 
Newbie Joined: Sep 2011 Posts: 16 Thanks: 0  Arithmetic Series
Hi, was wondering if anyone could help on these questions please? Would be appreciated!! 1) I have the first 3 terms, they are 3, 1, 1 and the common difference is +2. I need to show that n ? (2r5) = n(n4) r=1 2) The first term of an arithmetic sequence is 30 and the common difference is 1.5 It asked me to find the 25th term and I got 300. Then it tells me the rth term of the sequence is 0. * And asks me to find the value of r? Then it tells me the sum of the first n terms of the sequence is Sn. * And asks me to find the largest positive value of Sn? Any help would be great and if possible to show the working out as I have more questions like these. Thanks 
October 15th, 2011, 09:40 AM  #2  
Global Moderator Joined: Nov 2009 From: Northwest Arkansas Posts: 2,766 Thanks: 4  Re: Arithmetic Series Quote:
, where is the nth term, is the first term ( = 3 in this example), and is the difference ( = 2, as you have found) When we plug in the known values, this formula simplifies to . This is, effectively, the summand in the series. But the formula for a finite series is Substitute the known values into this formula and it will match exactly (after simplifying).  

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