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Lê Quốc Trần Anh Coordinator

03/08/2017 at 08:51
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2
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Find \(x,y\in Z\):

\(\dfrac{5}{x}-\dfrac{y}{3}=\dfrac{1}{6}\)




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  • ...
    Dao Trong Luan 03/08/2017 at 12:06

    \(\Rightarrow\dfrac{5}{x}=\dfrac{1}{6}+\dfrac{y}{3}\)

    \(\Rightarrow\dfrac{5}{x}=\dfrac{1}{6}+\dfrac{2y}{6}\)

    \(\Rightarrow\dfrac{5}{x}=\dfrac{2y+1}{6}\)

    \(\Rightarrow x\left(2y+1\right)=30\)

    But 2y + 1 is a odd => x is a even number

    => \(x\in\left\{-30;-10;-6;-2;2;6;10;30\right\}\)

    We have:

    x -30 -10 -6 -2 2 6 10 30
    2y+1 -1 -3 -5 -15 15 5 3 1
    y -1 -2 -3 -8 7 2 1 0

    So \(\left(x,y\right)=\left(-30;-1\right);\left(-10;-2\right);\left(-6;-3\right);\left(-2;-8\right);\left(2;7\right);\left(6;2\right);\left(10;1\right);\left(30;0\right)\)

  • ...
    baohong912006 04/08/2017 at 08:39

    ⇒5x=16+y3⇒5x=16+y3

    ⇒5x=16+2y6⇒5x=16+2y6

    ⇒5x=2y+16⇒5x=2y+16

    ⇒x(2y+1)=30⇒x(2y+1)=30

    But 2y + 1 is a odd => x is a even number

    => x∈{−30;−10;−6;−2;2;6;10;30}x∈{−30;−10;−6;−2;2;6;10;30}

    We have:

    x -30 -10 -6 -2 2 6 10 30
    2y+1 -1 -3 -5 -15 15 5 3 1
    y -1 -2 -3 -8 7 2 1 0

    So (x,y)=(−30;−1);(−10;−2);(−6;−3);(−2;−8);(2;7);(6;2);(10;1);(30;0)


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