Question

Qual é o 15° termo da PA (1,4,...) ?

Answer 1

$a_{1} = 1\\a_2 = 4\\ r = a_2 - a_1 = 4 - 1 \therefore r = 3$

Termo geral

$a_n = a_1 + (n-1)\cdot r \Rightarrow a_{15} = 1 + (15-1)\cdot 3 = 1 + 14\cdot 3 = 1 + 42$

$\therefore a_{15} = 43$