Question

ache a soma dos 20 primeiros termos da p.a (2,8,....)

Answer 1

an=a1+(n-1).r
a1=2
r=8-2=6
n=20

an=2+(20-1).6
an=2+19.6
an=2+114
an=116
A soma dos 20 primeiros termos
s20=(a1+an).n/2
S20=(2+116).20/2
S20=118.20/2
S20=2360/2
S20=1180