Tiga suku pertama barisan geometri mempunyai jumlah 10 1/2 dan hasil kalinya 27.Tentukan besar suku ke-8 barisan tersebut

[tex] a \times ar \times {ar}^{2} = 27 \\ {a}^{3} {r}^{3} = 27 \\ ar = 3 \\ \\ a + ar + {ar}^{2} = \frac{21}{2} \\ \frac{3}{r} + 3 + 3r = \frac{21}{2} \\ 2(6 + 3r) = 21r \\ 12 + 6r = 21r \\ 12 = 15r \\ r = \frac{12}{15} = \frac{4}{5} [/tex]


[tex]ar = 3 \\ a \frac{4}{5} = 3 \\ 4a = 15 \\ a = \frac{15}{4} [/tex]
[tex]u8 = {ar}^{7} = \frac{15}{4} ( \frac{4}{5} {)}^{7} = \frac{15}{4} ( \frac{16384}{78125} ) \\ = \frac{245760}{312500} = \frac{12288}{15625} [/tex]
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