Respuesta :

hartnn
Sum of n terms of a geometric series is
Sn = a1 (r^n-1)/(r-1)
a1 = 1st term = 4
r = common ratio = 12/4 = 3
so, the sum is
Sn = 4 (3^n-1)/(3-1) = 2(3^n-1)

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