Question

A soma do múltiplos de 3 compreendidos entre 10 e 50 (12...48)

Answer 1

a₁ = 12

an = 48

r = 3

48 = 12 + (n - 1) . 3 ---- 48 - 12 = (n - 1) . 3 ------ 36 = (n - 1) . 3

n - 1 = 36/3 ------ n - 1 = 12 -----  n = 12 + 1 ----- n = 13


S₁₃ = [(12 + 48) . 13]/2 --------- S₁₃ = [(60) . 13]/2 ----- S₁₃ = 780/2

S₁₃ = 390