Question

(-2,1,4,7...) a soma dos primeiros termos. Me ajudem ​

Answer 1

Boa tarde!

Dados:

a1 → -2

n → 45

An → ?

r → a2-a1 → 1-(-2) → 1+2 = 3

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An=a1+(n-1)·r

a45=-2+(45-1)·3

a45=-2+44·3

a45=-2+132

a45=130

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$\textit{Sn}=\frac{\mathrm{(a1+an)\times}n}{\mathrm{2}}$

$\textit{s15}=\frac{\mathrm{(-2+130)\times45}}{\mathrm{2}}$

$\textit{s15}=\frac{\mathrm{128.45}}{\mathrm{2}}$

$\textit{s15}=\frac{\mathrm{5760}}{\mathrm{2}}$

$\mathbf{s15}=\boxed{2880}$

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Att;Guilherme Lima