3 bilangan membentuk barisan geometri.jika hasil kalinya 216 dan jumlahnya 26.maka tentukan bilangan rasionya

a x b x c = 216
a + b + c = 26

mis. a = U1, b = U2 dan c = U3

a x b x c = 216
a x ar x ar² = 216
a³r³ = 216
ar = 6 .... pers. 1
a = 6/r ..... pers. 2

a + ar + ar²= 26
a + 6 + 6r = 26
a + 6r = 20
6/r + 6r = 20
-------------------- x r
6 + 6r² = 20r
6r² - 20r + 6 = 0
------------------------- : 2
3r² - 10r + 3 = 0
(r - 3)(3r - 1) = 0
r = 3 atau r = 1/3

jika r = 3, maka a = 6/3 = 2
jika r = 1/3, maka a = 6/1/3 = 18

bilangan tsb adalah
1) 2, 6, 18,...
2) 18, 6, 2,....

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