Question

calcule o numero de termos da p.a.(5,10,...,785).

Answer 1

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

Answer 2

an = a1 + (n - 1)r
785 = 5 + (n - 1)5
785 = 5 + 5n - 5
5n = 785
n = 785/5 =157