Jawabanmu

2014-05-02T18:36:14+07:00
U1 = 16
a = 16
U4 = 54
U4 = a r^3
54 = 16 r^3
r = 3/2
S4 = a ( 1 - r^4) / (1 - r)
     = 16 ( 1 - 81/16) / ( 1 - 3/2)
      = 16 (-65/16) / (-1/2)
       = 130 cm
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