Question

                                             (PA) (PG)
calcule o nono termo da PA : (3,5,7,.....)

Answer 1

Sabemos que:

$\boxed{a_n = a_1+(n-1)*r}\\\\ a_1=3\\\\ r = 5-3 = 2$


$a_9 = a_1+8r\\\\ a_9 = 3+8(2)\\\\ a_9 = 3+16\\\\ \boxed{a_9=19}$

Answer 2

An = a1 + (n-1).r

onde : 

a1 = 3
r = 5 - 3 = 2

a9 = 3 + (9-1).2
a9 = 3 + 8.2
a9 = 3 + 16
a9 = 19