U3=4,U8=256,deret geometri, U12?

u9/u3 = 256/4
ar^8/ar^2 = 64
r^6 = 64
r^6 = 2^6
r = 2
ar^2 = 4
a(2^2) = 4
4a = 4
a = 1

un = ar^(n-1)
u12 = 1 x 2^12-1
u12 = 1 x 2^11
u12 = 2048

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