Question 976774
{{{sum( (3(n-1))-2, n=1, 9)}}}

You can study the answer to see how it was obtained. The difference of 3 from one term to the next. 9 terms in the series. The -2 to start the series at -2. 
Note, it would look a bit different if we started at n=0, but many teachers prefer to see a result where the first term is referenced as n=1