Oh. I guess the point of the question was for you to find t12 first by using the general formula so that you could have the last term, which would allow us to use the simpler arithmetic series formula, i.e., n(t1+tn)/2 rather than n/2(2a+(n-1)d)
But I'd still like to know if there IS a way to find t12 with S12, just in case that comes up later or something.
Okay, so I know this should be really easy but my mind is just drawing a blank:
For each series, calculate t12 and S12
a) 37 + 41 + 45 + 49 + ...
Okay so I calculated S12 to be 708, and I know that's right.
For t12, I know I can easily find the general formula and then use that to find t12, but isn't there a faster way to do it knowing that the sum is 708?
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