Find Sum of First Five TermsDate: 03/26/2003 at 20:28:32 From: Jeff Subject: Math problem The 452nd term of an arithmetic sequence is -893 and the 84 is 27. Find the sum of the first five terms of the sequence. I could solve this if the first term were given, or the common difference, but I have neither so I will need your help. Date: 03/27/2003 at 00:06:04 From: Doctor Ian Subject: Re: Math problem Hi Jeff, Let's look at a smaller version of the same problem: The 6th term of an arithmetic sequence is -5, and the 3nd term is 1. What are the first given terms of the sequence? Now, it's true that I don't have the common difference, but I have something almost as good. I have the difference between two terms whose locations I know: __, __, 1, __, __, -5 If the common difference is d, then 1 + d + d + d = -5 1 + 3*d = -5 3*d = -6 d = -2 So now I _do_ know the common difference, and with that, I can get everything else. Does that make sense? Can you use the same reasoning to solve your problem? - Doctor Ian, The Math Forum http://mathforum.org/dr.math/ |
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