barisan geometri, suku awal=6, rasio=3, Un=486, tentukan banyak suku

Dik: U1= a = 6
r = 3
Un = 486
Dit: n =.....?
Jwb:
* Un = ar(pangkat) n-1
486 = (6)(3)n-1
6.3n-1 = 486
3n-1 = 486per 6
3n-1 = 81
3n-1 = 3⁴
n-1 = 4
n = 4 +1
n = 5

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