Posted by jae on Saturday, May 26, 2012 at 5:48am.
Find the sum of the first 25 terms of an arithmetic sequence whose 7th term is −247 and whose 18th term is −49.
- arithmetic - Reiny, Saturday, May 26, 2012 at 9:03am
7th term = -247 ---> a+6d = -247
18th term = -49 ---> a+17d =-49
11d = 198
d = 18
in a+6d = -247
a + 108 = -247
a = -355
sum(25) = (25/2)(-710 + 24(18)) = -3475
- arithmetic - harsh , Saturday, March 12, 2016 at 11:38pm
- math - harsh agrawal , Saturday, March 12, 2016 at 11:43pm
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