Bantu ya

U3 = a.r² = 4
U5 = a.r⁴ = 16

a.) a.r⁴ = 16
a.r² .r² = 16
4 .r² = 16
r² = 4
r = 2

a.r² = 4
a.2² = 4
a = 4/4
a = 1

b.) karena r>1
Sn = a(r^n -1)/r-1
S8 = 1(2^8 -1)/2-1
S8 = 256-1
S8 = 255

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