Question

Determine o a4 de uma PG, sabendo que o primeiro termo e 5 e que a razao e igual a 3

Answer 1

$a_n=a_1\cdot q^{n-1}$

$a_4=5\cdot3^{3}$

$a_4=5\cdot27~~\Rightarrow~~a_4=135$

Answer 2

$a_4=?\\n=4\\ a_1=5\\ q=3\\\\ a_n=a_1*q^{n-1}\\\\ a_4=5*3^{4-1}\to \\ a_4=5*3^{3}\to \\ a_4=5*27\to \\ a_4=135\\\\\\ PG(5,15,45,135)$