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Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

^ = pangkat

r = ^(5 - 3)√(U5 / U3)
r = ²√(3/27)
r = √(1/9)
r = +-1/3
r = -1/3

U8 = U5 . r^3
U8 = 3 . (-1/3)^3
U8 = 3 . (-1/27)
U8 = -1/9

Dik:
U3=27
U5=3

Dit: suku ke 8 ?

jwb:
[tex]un = a \times {r}^{n - 1} \\ {u}3 = a \times {r}^{3 - 1} = 27 \\ u3 = a \times {r}^{2} = 27.....(1)[/tex]
[tex]un = a \times {r}^{n - 1} \\ u5 = a \times {r}^{5 - 1} = 3 \\ u5 = a \times {r}^{4} = 3[/tex]
[tex]a \times {r}^{2} = 27 \\ a \times {r}^{4} = 3 \\ - - - - - - ( \div ) \\ {r}^{2} \div {r}^{4} = 27 \div 3 \\ {r}^{4 - 2} = 9 \\ {r}^{2} = 9 \\ r= \sqrt[2]{9} \\ r= (3 \times 3) \\ r= 3 [/tex]
[tex]r = 3 \\ sub = ...(1) \\ a \times {r}^{2} = 27 \\ a \times {3}^{2} = 27 \\ a \times (3 \times 3) = 27 \\ a \: \times 9 = 27 \\ a = \frac{27}{9} \\ a = 3[/tex]
[tex]ditanya =u8 \\ un = a \times {r}^{n - 1} \\ u8 = 3×3^8-1
u8=3×3^7
u8=3×2187=6561

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