Jawabanmu

2014-06-04T20:39:33+07:00
A = 64

U3 = 16
ar² = 16
64r² = 16
r² = 1/4
r = 1/2

S6 = a (1 - r^n)/1-r
     = 64 (1 - (1/2)^6)/ 1-1/2
     = 64 (1 - 1/64) / 1/2
     = 128 (63/64)
     = 2.63
     = 126
63/64 itu dapet dr mn?
1 - 1/64 -----> 64/64 - 1/64 -------> 63/64
lalu 1/2 ny ?
2014-06-04T20:43:15+07:00
U₁ = a = 64 ; U₃ = 16
Un =  ar^{n-1}
U₃ = ar²
16 = 64r²
r² = 1 / 4
r = 1/2, maka r < 1

 S_{n}= \frac{a(1- r^{n}) }{1-r} \\  S_{6}= \frac{64(1-  \frac{1}{2} ^{6}) }{1- \frac{1}{2} } \\ = \frac{64(1- \frac{1}{64}) }{ \frac{1}{2} } \\ = (64-1)2 \\ =126