What is the sum of the arithmetic sequence 137, 125, 113 …, if there are 38 terms?

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Answer 1 · 2016-05-15T12:09:13

Sum $=-3230$

Given first term $a_1=137$
common difference $=-12$

number of terms $n=38$

compute the 38th term
$a_38=a_1+(n-1)*d$

$a_38=137+(38-1)*(-12)$

$a_38=-307$

Compute sum $S_38$

$S_38=n/2*(a_1+a_38)$

$S_38=38/2*(137+(-307))$

$S_38=-3230$

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