Diketahui deret geometri 4+2+1+1/2 Tentukan rasio, suku ke 12 dan hitunglah 12 suku pertamanya

Bab Barisan dan Deret
Matematika SMP Kelas VIII

r = U2 : U1
  = 2 : 4
  = 1/2

U12 = a . r¹¹
        = 4 . (1/2)¹¹
        = 4 . 1/2.048
        = 1/512

Sn = (a . (1 - rⁿ)) / (1 - r)

S12 = (4 . (1 - (1/2)¹²) / (1 - 1/2)
       = (4 . (4.096/4.096 - 1/4.096)) / (1/2)
       = 4 . (4.095/4.096) . 2
       = 4.095/512
       = 7 511/512