Question

Dada a PA (1,5,9,13...) Qual é o centésimo termo dessa PA ?

Answer 1

a1 = 1
r = 5-1 = 4
n = 100
an = a1+(n-1)*r
an = 1+(100-1)*4
an = 1+99*4
an = 1+396
an = 397 

Answer 2

$An = a_{1} + (n -1) .r$

r = a2 -a1
r = 5 -1  → 4

a100 = 1 + (100 -1) . 4
a100 = 1 + 99 . 4
a100 = 397