Question

P.A (2,5,8,...20)possui razao igual a e tem termos. A soma dos termos dessa P.A é?

Answer 1

Bom Dia!

Dados;

A1 → 2

An → 20

R → a2-a1 → 5-2 = 3

N → ?

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An=a1+(n-1)·r

20=2+(n-1)·3

20=2+3n-3

-3n=2-3-20

-3n=-1-20

-3n=-21

n=-21/-3

n=7

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

$\textit{S7}=\frac{\mathrm{(2+20).7}}{\mathrm{2}}$

$\textit{S7}=\frac{\mathrm{22.15}}{\mathrm{2}}$

$\textit{S7}=\frac{\mathrm{330}}{\mathrm{2}}$

$\mathbf{S7}=\boxed{165}$

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Att;Guilherme Lima

Answer 2

Resposta:

a soma geral e de 78

Explicação passo-a-passo:

r=a2-a1

r=5-2

r=3

2,5,8,11,14,17,20

2+5+8+11+14+17+20

8+8+11+1417+20

16+11+14+17+20

27+14+17+20

41+17+20

58+20

78