Question

detetmine a soma dos dezoito termos da p.a 1 4 7

Answer 1

Boa noite!

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Dados;

A1 → 1

N → 18

R → a2-a1 → 4-1 = 3

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An=a1+(n-1)·r

a18=1+(18-1)·3

a18=1+17·3

a18=1+51

a18=52

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$\textit{Sn}=\frac{\mathrm{(A1+An).n}}{\mathrm{2}}$

$\textit{S15}=\frac{\mathrm{(1+52).18}}{\mathrm{2}}$

$\textit{S15}=\frac{\mathrm{53.18}}{\mathrm{2}}$

$\textit{S15}=\frac{\mathrm{954}}{\mathrm{2}}$

$\mathbf{S15}=\mathbf{477}$

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Att;Guilherme Lima