Find the sum of the first eight terms of the arithmetic progression -23, -20
| July 18, 2021 | education
Find the sum of the first eight terms of the arithmetic progression: a) -23, -20
Let’s find the difference of the progression: d = – 20 – (- 23) = – 20 + 23 = 3.
Let’s find the value of the eighth term of the progression.
a8 = – 23 + 3 * 7 = – 23 + 21 = – 2.
Let’s find the sum of the first eight terms.
S8 = (a1 + a8) / 2 * 8 = (- 23 – 2) / 2 * 8 = – 12 * 8 = – 96.
Answer: S8 = – 96.
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