diketahui barisan geometri dengan s2=72 dan s4=80. hitung nilai u5.

a + ar = 72
a + ar + ar^2 + ar^3 = 80
(a + ar) + r^2(a + ar) = 80
72 + r^2 (72) = 80
r^2 (72) = 8
r^2 = 8/72
r = 1/3

a + ar = 72
a + a(1/3) = 72
(4/3)a = 72
a = 72 . 3/4
= 54

U5 = ar^4
= 54 . (1/3)^4
= 54 . 1/81
= 6/9
= 2/3