3. Jika U4 = 10/9 dan U6 = 10/81 Tentukan a dan r !

Bab Barisan dan Deret
Matematika SMP Kelas IX

r = (U6 : U4)^1/(6 - 4)
  = (10/81 : 10/9)^(1/2)
  = (10/81 x 9/10)^(1/2)
  = (9/81)^(1/2)
  = (1/9)^(1/2)
  = 1/3

a = U4 : r³
  = 10/9 : (1/3)³
  = (10/9) x 27
  = 30