Question

Calcule a soma dos trintas primeiros termos da P.A (3,8,13,18.. )

Answer 1

$a_1 = 3\\ r = 5\\ n = 30\\ a_n = ?\\ S_n = ?\\ \\ a_n = a_1 + (n-1).r\\ a_n = 3 + (30 - 1).5\\ a_n = 3 + 145\\ a_n = 148\\ \\ S_n = \frac{(a1\ +\ an).n}{2}\\ \\ S_{30} = \frac{(3\ +\ 148).30}{2}\\ \\ S_{30} = 151.15\\ S_{30} = 2265$

Resposta: 2265