SOLUTION: How many terms of the arithmetic sequence -12,-3,6... Must be added to arrive at a sum of 363?

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Question 928433: How many terms of the arithmetic sequence -12,-3,6... Must be added to arrive at a sum of 363?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a%5Bn%5D=-21%2B9n
S%5Bn%5D=%28n%2F2%29%28a%5B1%5D%2Ba%5Bn%5D%29
363=%28n%2F2%29%28-12-21%2B9n%29
726=n%289n-33%29
9n%5E2-33n=726
3n%5E2-11n-242=0
%28n-11%29%283n%2B22%29=0
Only the positive solution makes sense here.
n-11=0
n=11terms