Question

Calcule a soma dos 7 primeiro termo da P.G(4,-12,36)

Answer 1

q=36/-12=-3 
sn=a1(q^7-/q-1 
sn=4[(-3)^7-1]-4
sn=-1(-2187-1)
sn=-1(-2188)=2118

Answer 2

(4, - 12 , 36, ...)

a₁ = 4

q = - 12/4  ----- q = - 3

Sn = [a₁ . (qⁿ -1)]/q - 1 ------ S₇ = [4 . ((-3)⁷ - 1 )]/(- 3 - 1) ----

S₇ = [4 . ((-3)⁷ - 1)]/(- 4) ------ S₇ = [4 .(- 2187 - 1)]/(- 4) -----

S₇ = [4 . (- 2188]/(- 4) ----- S₇ = - 8752/(- 4) ----- S₇ = 2188

(4, - 12, 36, - 108, 324, - 972, 2916)