Question 884757

Find the sum of the terms of the following arithmetic progressions.

-10, -7, -4,.. To 12 terms.
<pre>
{{{S[n] = (n/2)(2a[1] + (n - 1)d))}}}, with:
{{{S[n]}}} being the sum of the 12 arithmetic terms
n being the number of terms
{{{a[1]}}} being the 1st term, or term 1
d being the common difference

Thus, {{{S[n] = (n/2)(2a[1] + (n - 1)d))}}} becomes: 
{{{S[n] = (12/2)(2(- 10) + (12 - 1)3)}}}
{{{S[n] = 6(- 20 + (11)3)}}}
{{{S[n] = 6(- 20 + 33)}}}
{{{S[n] = 6(13)}}}
{{{highlight_green(highlight_green(S[n] = 78))}}}
You can do the check!! 

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