Find the sum of the first 25 terms of the arithmetic sequence: 7,19,31,43,...
We use the formula: S = a1 + (n-1)d ; where a1 is the first term, n is the number of terms we want to add, and d is the common difference of the sequence.
S = 7 + (25 - 1)(12) = 7 + 24 x 12 = 7 + 288 = 295
Hope that helps.
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