Jawabanmu

2014-05-04T14:25:27+07:00
U3= a.r^2=2
U7= a.r^6=32. maka,

a.r^2.r^4=32
2.r^4=32
r^4=32/2 = 16
r=2

a.r^2=2 --> a.4=2 ---> a=2/4 = 1/2

Sn = a(r^n-1)/r-1
Sn= ½(2^9-1)/2-1 -----> 511,5