The first term of an arithmetic sequence is 12 and the common difference is 9. Find the sum of the first 24 terms.
Remember: With first term a, common difference d and n terms, the sum is n[2a + (n − 1)d] ÷ 2.
The first term of an arithmetic sequence is −3 and the common difference is 1. Find the sum of the first 9 terms.
The first term of an arithmetic sequence is 10 and the common difference is 2. Find the sum of the first 18 terms.
The first term of an arithmetic sequence is −9 and the common difference is −2. Find the sum of the first 18 terms.
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