Question

A soma dos 6 primeiros termos da PA (1,5, ...) é: *
(А) 58
О (В) 40
(C) 50
О(D) 66
О(E) 32​

Answer 1

Resposta:

$\red{ \boxed{ \boxed{ \boxed{ \boxed{ \boxed{d) = 66}}}}}}$

Explicação passo-a-passo:

primeiro temos que encontrar o valor da razão dessa P.A

r = a2 - a1

r = 5 - 1

r = 4

agora temos que encontrar o valor de a6.

$</strong><strong>a_</strong><strong>{n} = </strong><strong>a_</strong><strong>{1} + (n - 1) \times r \\ </strong><strong>a_</strong><strong>{6} = 1 + (6 - 1) \times 4 \\ </strong><strong>a_</strong><strong>{6} = 1 + 5 \times 4 \\ </strong><strong>a_</strong><strong>{6} = 1 + 20 \\ </strong><strong>a_</strong><strong>{6} = 21$

agora que encontramos o valor de a6 iremos encontrar a soma dos 6 primeiros termos.

$</strong><strong>s_</strong><strong>{n} = \frac{(</strong><strong>a_</strong><strong>{1 }+ </strong><strong>a_</strong><strong>{n}) \times n}{2} \\ </strong><strong>s_</strong><strong>{6} = \frac{(1 + 21) \times 6}{2} \\ </strong><strong>s_</strong><strong>{6} = \frac{22 \times 6}{2} \\ </strong><strong>s_</strong><strong>{6} = \frac{132}{2} \\ \red{ \boxed{ \boxed{ \boxed{</strong><strong>s_</strong><strong>{6} = 66}}}}$

espero ter ajudado :)