suatu barisan geometri diketahui U4= 8/3 dan U3+U5=20/3. tentukan suku pertama barisan tsb. tlong skarangg

(U3+U5) / U4 = 20/3 : 8/3
(ar^2+ar^4) / ar^3 = 20/8
ar^2(1+r^2) / ar^3 = 5/2
(1+r^2) / r = 5/2
1 + r^2 = 5/2 r
---------------------(x2)
2+2r² = 5r
2r² - 5r + 2 = 0
(2r-1)(r-2) = 0
2r-1 = 0 atau r-2 = 0
r = 1/2 atau r = 2

ar³ = 8/3
a(1/2)³ = 8/3 atau a(2)³ = 8/3
a(1/8) = 8/3              8a = 8/3
a= 64/3                      a = 1/3