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For the arithmetic sequence beginning with the terms {9, 14, 19, 24, 29, 34 ...}, what is the sum of the first 23 terms?

User Shaw
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1 Answer

5 votes

Answer:

1472

Explanation:

The sum of n terms of an arithmetic sequence is


S_(n) =
(n)/(2) [ 2a₁ + (n - 1)d ]

where a₁ is the first term and d the common difference

Here a₁ = 9 and d = 19 - 14 = 5 , thus


S_(23) =
(23)/(2) [ (2 × 9) + (22 × 5) ]

= 11.5 (18 + 110) = 11.5 × 128 = 1472

User Dchhetri
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