Question

pergunta ; calcule o número de termos de P.A.(5,10,...,785)

Answer 1

$Dados\to \left\{\begin{array}{ccc}Termo\ Geral \to a_n = a_1+(n-1)r\\a_1=5\\a_n=785\\r = 5\\n=?\end{array}\right$

$Resolu\c{c}\~ao\to \left\{\begin{array}{ccc}a_n=a_1+(n-1)r\\\\785 = 5+(n-1)5\\\\785 = 5+5n-5\\\\5n = 785\\\\n = \frac{785}{5}\\\\\boxed{n = 157\ termos} \end{array}\right$

Espero ter ajudado. :))

Answer 2

Nesta PA:

a1 = 5
an = 785
r = 5

De acordo com a Fórmula do Termo Geral:

$a_n=a_1+(n-1)r\\ \\ 785=5+(n-1)5\\ \\ n-1=\frac{785-5}{5}\\ \\ n-1=156\\ \\ n=157 \ termos$