Question

62) Calcule a soma dos 16 primeiros termos da P.A. (3, 11, 19,...).​

Answer 1

Resposta:

$sn = \frac{(an + a1) \times n}{2} \\ \\ an = a1 + (n - 1) \times r$

r=11-3

r=8

a16=3+(16-1)*8

a16=3+15*8

a16=3+120

a16=123

$s16 = \frac{(a16 +a1) \times 16 }{2} \\ s16 = (123 + 3) \times 8 \\ s16 = 126 \times 8 \\ s16 = 1008$