Jawabanmu

2014-06-08T22:44:47+07:00
U1 + U2 = 45 ⇔ a + ar = 45 ⇔ a(1+r) = 45
U3 + U4 = 20 ⇔ ar² + ar³ = 20 ⇔ ar²(1+r) = 20
ar²(1+r)  20
a(1+r)         45
r² = 4/9 ⇔ r = - 2/3 atau r = 2/3
untuk r = -2/3 ⇒ a(1+r) = 45 ⇔a(3/3 - 2/3) = 45 ⇔ a = 45/(1/3) = 135
untuk r =  2/3 ⇒ a(1+r) = 45 ⇔ a(3/3 + 2/3) = 45 ⇔ a = 45/(5/3) = 27
3 4 3