Question

Dada a p.a. (7,11,15,......) determine a ¹⁸

Answer 1

a1=7

r=4

n=18

an=?

$an = a1 + (n - 1) \times r \\ an = 7 + (18 - 1) \times 4 \\ an = 7 + 17 \times 4 \\ an = 7 + 68 \\ an = 75$