Jawabanmu

2014-06-13T20:32:41+07:00
 U_{1} = a r^{0} = 2
 U_{5} = a r^{0} .  r^{4}
       2 .  r^{4} = 162
                  r^{4}  =  \frac{162}{2}  = 81
                 r = 3

a  r^{0} = 2
a 3^{0} = 2
a = 2
jadi rumus suku ke - n = 2 .  3^{n-1}
2014-06-13T20:41:12+07:00
A. barisan tersebut 2, - 6, 18, - 54, 162 atau 2, 6, 18, 54, 162
b. Un = 2 (-3)^{n-1} atau   U_{n}=2 (3)^{n-1}