jumlah 6 suku pertama dari deret geometri 2/3+2/9+2/27 adalah

r (rasio) = U2 : U1 = 2/9 : 2/3 = 2/9 x 3/2 = 1/3
a = 2/3
n = 6
S6 = a(r^n - 1)
        -------------
             (r -1)
     = 2/3 ((1/3)^6 - 1)
        ---------------------
              (1/3 - 1)
     = 2/3 (1/729 - 1)
       --------------------
           (1/3 - 3/3)
     = 2/3 (1/729 - 729/729) :
        ----------------------------
                   (-2/3)
     (2/3 dan -2/3 dapat di coret/ dibagi)
    = 1 (-728/729)
       ----------------
              -1
S6 = 728/729

Maaf kalau salah