Question

CALCULE A SOMA DOS 80 PRIMEIROS TERMOS DA PA( 10,6,2,...)

Answer 1

(10, 6, 2, ...)

a₁ = 10

r = 6 - 10 ----- r = - 4

an = a₁ + (n - 1) r -------- a₈₀ = 10 + (80 - 1) . (- 4) ----- a₈₀ = 10 + 79 . ( - 4)

a₈₀ = 10 - 316 ----- a₈₀ = - 306

Sn = (a₁ + an) . n/2 ---- S₈₀ = [(10+ (-306)) . 80]/2 ------ S₈₀ = (10 - 306) . 40

S₈₀ = - 296 . 40 ------- S₈₀ = - 11840