Jawabanmu

2014-02-09T23:06:31+07:00
Sn = a(1 - r^n)/(1-r)
S6 = a(1 - 1/2^6)/(1-1/2)
189 = a(1 - 1/64)/1/2
189 = a x 63/64 x 2/1
189 = a x 63/32
a = 189 x 32/63
a = 96
S1 = a = 96

S3 = a(1 - 1/2^3)/(1-1/2)
S3 = 96(1 - 1/8)/1/2
S3 = 96 x 7/8/12
S3 = 168


maaf ya @Ivanfadillah82 soalnya salah ^.^