Question

Calcule o 30° termo da PA (4,8,12,...) e calcule a soma dos seus 30 termos?

Answer 1

PA de razão igual a 4 . a30=a1+(30-1)x 4 
a30= 4+29x4      a30=4+116   a30=120

S30=(a1+a30)x30/2
S30=(120+4)x30/2      S30=1860

Answer 2

a1= 4

r= 8 - 4 = 4

an= a1 + (n - 1) • r

a30= 4 + (30 - 1) • 4

a30= 4 + 29 • 4

a30= 4 + 116

a30= 120

sn= (a1 + an) • n/2

sn= (4 + 120) • 30/2

sn= 124 • 30/2

sn= 62 • 30

Sn= 1860