Jawabanmu

2014-03-27T20:30:57+07:00
6,9,12,....,96

a+(n-1).b = Un
6+(n-1).3 = 96
6+3n-3 = 96
3+3n = 96
n = 31

Sn =  n÷2(a+Un)
S31 = 31÷2(3+96)
S31 = 31÷2(102)
S31 = 31×51
S31 = 1581


2014-03-27T21:03:28+07:00
6 + 12 + ... + 96 = 816