Diketahui deret artimatika 1+3½+6+..... Apabila Sn=208, tentukanlah n dan Un.
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Pertanyaan
Diketahui deret artimatika 1+3½+6+..... Apabila Sn=208, tentukanlah n dan Un.
1 Jawaban
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1. Jawaban caturprasetyow
a=1
b=3
Sn=208
[tex] < = > \frac{1}{2} n(2a + (n - 1)b = 208 \\ < = > \frac{1}{2} n(2 + (n - 1)3 = 208 \\ < = > \frac{1}{2} n(2 + 3n - 3) = 208 \\ < = > \frac{1}{2} n(3n - 1) = 208 \\ < = > \frac{3}{2} {n}^{2} - \frac{1}{2} n = 208 \\ < = > \frac{3}{2} {n}^{2} - \frac{1}{2} n - 208 = 0 \\ < = > 3 {n}^{2} - n - 416 = 0 \\ < = > [/tex]