Question

Qual o décimo oitavo termo da P.A ( 5,8,11,14,..)

Answer 1

a18 = a1 + 17r → a18 = 5 + 17 . 3 → a18 = 5 + 51 → a18 = 56

Answer 2

$A_1 = 5 \\ r = 3 \\\\\\ A_n = A_1 + (n-1) \cdot r \\ A_{18} = 5 + (18-1) \cdot 3 \\ A_18 = 5 + 17 \cdot 3 \\ A_{18} = 5 + 51 \\ A_{18} = 56$