Question

Sa se determine Sn a progresiei geometrice stiind ca b1=8 b3=2 n=8

Answer 1

Răspuns:

• bn = b1 × q^(n-1)

b3 = b1 × q^2 = 8 × q^2 = 2

q^2 = 2/8 = 1/4

q = 1/2

• Sn = b1 × (q^n-1) / (q - 1)

S8 = 8 × [(1/2)^8 - 1] / (1/2 - 1) =

        8 × (1/256 - 1) / (-1/2) =

        8 × (-255/256) / (-1/2) =

        (-255/32) × (-2) =

       255/16 =

        15 intregi 15/16