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find the sum of the first 50 terms of the arithmetic sequence -15,-9,-3,3....
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You will need the formula: \[\sum_{k=1}^{n}k = \frac{1}{2}n(n+1)\] Write down the sequence in terms of an index, then put it in a sum and simplify.
i cant get it
Let's say you take as index n=1,2,3,... so your sequence is \(a_1 = -15\) \(a_2 = -9\) \(a_3 = -3\) ... so what is a general term for a_n ?
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