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find the sum of the first 15 terms of the arithmetic sequence 17,12,7 with solution​

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Step-by-step explanation:

17, 12, 7, ...

a1 = 17

d = 12 - 17 = -5

n = 15

Sn = n/2 (2a1 + d (n - 1))

S15 = 15/2 (2 (17) + (-5) (15 - 1))

S15 = 15/2 (34 + (-70))

S15 = 15/2 (-36)

S15 = -270

I hope this helps

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