Question

A P.A. (2,6,10...) tem doze termos . calcule a soma

Answer 1

dados:

a1 = 2
r = 6 - 2 = 4
n = 12
an = ?
sn = ?

an = a1 + (n - 1)r
a12 = 2 + (12 - 1)4
a12 = 2 + 11.4
a12 = 2 + 44
a12 = 46

sn = (a1 + an)n/2
sn = (2 + 46)12/2
sn = 48.12/2
sn = 24.12
sn = 288

R.: sn = 288