Jawabanmu

2014-06-11T10:46:06+07:00
U4 = a x r³
108 = 4 x r³
108 : 4 = r³
    27   = r³
    r      = ∛27
    r      = 3

S5 = a ( r^{5} - 1) / r - 1
S5 = 4 (  3^{5} - 1) / 3-1
S5 = 4 ( 243 - 1) / 2
S5 = 4 x 242 / 2
S5 = 484


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