In an arithmetic progression, a1 = -12, d = 4. Find the twenty-second term and the sum of the first twenty-two terms
| September 20, 2021 | education
We will use the formulas for the nth term and the sum of n terms of the arithmetic progression, substitute in them the values of the first term of the series a1 = – 12, and the difference d = 4.
an = a1 + (n – 1) * d.
a22 = – 12 + (22 – 1) * 4 = – 12 + 21 * 4 = – 12 + 84 = 72.
Sn = (a1 + an) n / 2.
S22 = (a1 + a22) 22/2 = (- 12 + 72) * 11 = 60 * 11 = 660.
Answer: a22 = 72; S22 = 660.
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