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chautieuthupp

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riverflowsinyou1

Giải

chautieuthupp said:
3.Tìm x, y thuộc Z
1/18 < x/12 < y/9 < 1/4
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BCNN(18;12;9;4)=36
\Rightarrow 2<x.3<y.4<9
2<(6;8);(3;8);(3;4)<9
Mà x.3 chia hết cho 3 y.4 chia hết cho 4 \Rightarrow x=1;y=1 ( x=2;y=2);(x=1;(y=2)
 
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S

san1201

ta có [TEX]\frac{1}{18}<\frac{x}{12}<\frac{y}{9}<\frac{1}{4}[/TEX]
\Leftrightarrow[TEX]\frac{2}{36}<\frac{3x}{36}<\frac{4y}{36}<\frac{9}{36}[/TEX]
\Leftrightarrow [TEX]2<3x<4y<9[/TEX]
mặt khác x,y thuộc Z nên [TEX]\left[\begin{matrix} 3x=3;4y=4\\ 3x=6;4y=8\end{matrix}\right[/TEX]\Rightarrow[TEX]\left[\begin{matrix}x=1;y=1\\ x=2;y=2\end{matrix}\right[/TEX]
 
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