Jawabanmu

2014-03-21T21:34:09+07:00
U1 = 2
U5 = U1 .r^4 = 2 . r^4 = 162
r^4 = 81
r = 3

Sn = U1 .(r^5 - 1)/ r-1
= 2 . (3^5 - 1) / 3 - 1
= 3^5 - 1
= 243 - 1 = 242
2014-03-21T21:42:03+07:00
U1 = 2 cm (a)
U5 = 162 cm (a*r∧n-1) = (a*r∧5-1) = (a*r∧4)
(a*r∧4)/a = r∧4
162 / 2 = 81
r∧4 = 81
r = 3

Sn = (a(r∧n-1)) / (r-1)
S5 = (2(3∧5-1)) / (3-1)
S5 = (2 * 242) / 2
S5 =  242 cm