Question

Qual o número de termos da P.G (-1/120, 1/60, -1/30, ..., 64/15)?

Answer 1

a1 = - 1/120

a2 = 1/60

a3 = -- 1/30

q = ( 1/60) : ( - 1/120) ou (1/60 ) * ( - 120/1) = -120/60 = -2 ***

an = 64/15

an = a1 . qⁿ⁻¹

64/15 = ( - 1/120) * ( -2)ⁿ⁻¹

64/15 : ( - 1/120) = ( - 2)ⁿ⁻¹

64/15 * ( - 120/1 = ( -2)ⁿ⁻¹

- 7680/15 = ( - 2)ⁿ⁻¹

- 512 = ( - 2)ⁿ⁻¹

( - 2)ⁿ⁻¹ = ( -2)⁹

n - 1 = 9

n = 9 + 1

n = 10 ***** resposta