Question

a soma dos vinte primeiro termo da PA (4,10)

Answer 1

A20=4+(20-1)6
A20=4+19*6
A20=4+114
A20=118

Soma dos termos:

S20=(4+118)20/2
S20=122*20/2
S20=2440/2
S20=1220

Soma: 1220

Answer 2

An=a1+(n-1).r
A20=4+(20-1).6
A20=4+19.6
A20=4+114
A20=118
SN=(a1+an).n/2
S20=(4+188).20/2
S20=192.10
S20=1920