Jawabanmu

2014-03-24T11:40:46+07:00
S2=ar=6....S6=ar^5=96...6r^5=96...r^5=16...r=2....a=3 ...S8=(3 (2^8-1))/2-1=765
2014-03-24T12:05:00+07:00
 U_{2} = 6
 U_{6} = 96
ditanya :  S_{8} = ?
b = \frac{96-6}{6-2}
   = 22,5
 U_{2} = a+b
6 = a + 22,5
a = -16,5

 S_{8} =  \frac{8}{2}(2.(-16,5) + (7)22,5) = 4 (-33 + 157,5)

S_{8} = 498

semoga membantu :)