Jawabanmu

2014-03-09T18:01:04+07:00
a,b,c,nanti saat di barisan aritmatika b+4
a+b+c = 30
b= a.r^n-1,
6=a.r^1 = 6/r = a , c = a.r^n-1= 6/r . r^2 = 6.r
maka. a + b + c = 30
           6/r + 6 + 6r = 30
          6/r + 6r = 24
            6r+ 6 = 24
             6r = 18
            r = 3
             

a= 2
b = 6
c = 18
r= 3
jika b +4 = 6+ 4 =10,maka a+b+c= 30 :)
sehingga 2 x 6 x18 =156 :)

2014-03-09T18:08:07+07:00
Mis A B C -geometri
r>1

A+B+4+C=30
S3=3/2(A+C)
30=3/2(A+C)
20=A+C

B+4+20=30
B=6

nah sekarang pake permisalan
r>1 
mis r=2
berarti
A B C= 3 6 12
3+6+4+12=25≠30

mis r=3
A B C=2 6 18
2+6+4+18=30=30 --- benar
jadi 
ABC=2×6×18=216