pada barisan aritmetika, s3=24 dan s6= 75.tentukan u4 pada barisan tersebut
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Penjelasan dengan langkah-langkah:
[tex]s(3) = 24 \\ s(6) = 75 \\ \\ s(3) = \frac{3}{2}(2a + (3 - 1) \: b) \\ 24 = \frac{3}{2}(2a + 2b) \\ 24 = \frac{3}{2}(2)(a + b) \\ 24 = 3(a + b) \\ a + b = 8 \: (i) \\ \\ s(6) = \frac{6}{2}(2a + (6 - 1)b) \\ 75 = 3(2a + 5b) \\ 2a + 5b = 25 \: (ii) \\ \\ a + b = 8 \: | \times 2| \\ 2a + 5b = 25 \: | \times 1| \\ \\ 2a + 2b = 16 \\ 2a + 5b = 25 \: (dieliminasi) \\ \\ - 3b = - 9 \\ b = 3 \\ \\ a + b = 8 \\ a + 3 = 8 \\ a = 5 \\ \\ u(4) = a + (4 - 1)b \\ = 5 + 3b \\ = 5 + 3(3) \\ = 5 + 9 \\ = 14 [/tex]
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