Question

Calcule a soma dos 45 termos iniciais da PA (5,18,31...)

Answer 1

(5, 18, 31, ...)

a₁ = 5

r = 18 - 5 ------- r = 13

an = a₁ + (n - 1) r ----- a₄₅ = 5 + (45 - 1) . 13 ----- a₄₅ = 5 + (44) . 13

a₄₅ = 5 + 572 ------ a₄₅ = 577

Sn = [(a₁ + an). n]/2 ----- S₄₅ = [(5 + 577) . 45]/2 -------- S₄₅ = [(582) . 45]/2

S₄₅ = 26190/2 ----------- S₄₅ = 13095