Jawabanmu

2014-05-21T20:56:24+07:00
Rasionya(r)= 2 memakai perbandingan.
a.r=6
a.2=6
a=3
S4= a(r pangkat n - 1) / r-1 = 3(2 pangkat 4 -1) / 2-1 = 3 x 15 : 1 = 45
jadi S4= 45

2014-05-21T20:56:46+07:00
Deret geometri
Un = a  r^{n-1}

U2 = a r
6 = a r

U5 = a  r^{4}
48 = a  r^{4}
48 = a r  r^{3}
48 = 6  r^{3}
8 =  r^{3}
r = 2

6 = a r
6 = a 2
a = 3

Sn =  \frac{a( r^{n} -1)}{r-1}

S4 =  \frac{3( 2^{4} -1)}{2-1}
S4 = 3(15) =45