Jawabanmu

2014-02-17T17:38:07+07:00
U3 =  ar^{2} = 12
u5 = ar^{4} = 48

u5 : u3 = ar^{4}  ar^{2} = 48 : 12
            r^{2} = 4
            r = 2 atau -2

a) karena r yang diminta < 1,pakai r = -2.
u3 =  ar^{2} = a x (-2) ^{2} = 12
a = 3

b) u10 =  ar^{9} = 3 x  (-2)^{9} = 3 x (-512) = -1536

c) 5 bil pertama : 3,-6,12,-24,48