SOLUTION: find the 30m th term as well as the sum of the 1st twenty terms of each of the following arithmetic sequences: i) -15; -8; -1

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Question 1040095: find the 30m th term as well as the sum of the 1st twenty terms of each of the following arithmetic sequences:
i) -15; -8; -1
Answer by josgarithmetic(39617) About Me  (Show Source):
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index n;
-15%2B7%28n-10%29, general term.

The term at n=30 is -15%2B7%2830-1%29=-15%2B7%2A29=188.

The sum of first 20 terms
%2820%2F2%29%28-15%2B%28-15%2B%287%2A%2820-1%29%29%29%29 according to the summation formula for arithmetic series