Question

Calcule a soma dos 9 termos da PA (1, 3, 5, ...,17)

Answer 1

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PA = (1;3;5;...;17)

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R = a² - a¹

R = 3 - 1

R = 2

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aⁿ = a¹ + (n - 1)R

a⁹ = 1 + (9 - 1)2

a⁹ = 1 + 8(2)

a⁹ = 1 + 16

a⁹ = 17

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Sn = (a¹ + aⁿ)n/2

S⁹ = (1 + 17)9/2

S⁹ = (18)9/2

S⁹ = 162/2

S⁹ = 81 ← Resposta

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Att: MarcosPCV