Question

calcule a soma dos 8 primeiros termos da pa ( 1,3,5....)

Answer 1

Calcule a soma dos 8 primeiros termos da pa ( 1,3,5....)
n = 8
a1 = 1
r = 3-1 = 2
an = a1+(n-1)*2
an = 1+(8-1)*2
an = 1+7*2
an = 15
Sn = (a1+an)*n/2
Sn = (1+15)*8/2
Sn = 16*4
64
Verificando: 1+3+5+7+9+11+13+15

Answer 2

Encontrando o ultimo termo considerado
$a_{8} = 1 + (8-1).2$
$a_{8}= 1+7.2$
$a_{8}= 15$

A soma dos termos
$S_{n} = \frac{8 ( 1+15)}{2}$
$S_{n}= \frac{8.16}{2}$
$S_{n} = \frac{128}{2}$
$S_{n} = 64$