Question

Determine o trigésimo termo da P.A (1,5,9...)

Answer 1

an = a1 + (n-1).r
a2 = a1 + (2-1).r
5 = 1 + 1.r
5 = 1 + r
r = 5 - 1
r = 4

an = a1 + (n-1).r
a30 = a1 + (30-1).r
a30 = 1 + 29.4
a30 = 1 + 116
a30 = 117

Answer 2

$P.A (1,5,9...)\\\\ a_1=1\\r = 9-5 = 4\\ n=30\\ a_n=?\\\\\\ a_n=a_1+(n-1)*r\\\\\\ a_{30}=1+(30-1)*4\to\\\\ a_{30}=1+29*4\to\\\\ a_{30}=1+116\to\\\\ \large\boxed{a_{30}=117 }$