Question

2) Exercício de PA

O vigésimo elemento da sucessão aritmética(12,17,22,27,...) é?​

Answer 1

$\{a_1,a_2,a_3,a_4,\cdots\}\equiv\{12,17,22,27,\cdots\}$

$\boxed{a_n=a_k+(n-k)r}$

$a_2=a_1+r\ \Longrightarrow r=a_2-a_1=17-12\ \therefore\ \boxed{r=5}$

$a_{20}=a_1+19r\Longrightarrow a_{20}=12+19(5)\ \therefore\ \boxed{a_{20}=107}$