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Lê Quốc Trần Anh Coordinator

10/06/2018 at 06:31
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Find x,y,z satisfys: \(\dfrac{x}{8}=\dfrac{y}{3}=\dfrac{z}{10}\) and xy + yz + zx = 1206




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    Alone 14/06/2018 at 01:07

    \(\dfrac{x}{8}=\dfrac{y}{3}=\dfrac{z}{10}\Rightarrow\dfrac{x^2}{64}=\dfrac{xy}{24}=\dfrac{yz}{30}=\dfrac{zx}{80}=\dfrac{xy+yz+zx}{24+30+80}=\dfrac{1206}{134}=9\)

    \(\Rightarrow x^2=64.9=8^2.3^2\Rightarrow x=\pm24\)

    With x=24 then y=24:8.3=9;z=30

    With x=-24 then y=-9;z=-30

    Lê Quốc Trần Anh selected this answer.
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    Nguyễn Mạnh Hùng 15/06/2018 at 01:35

    We have:

    \(\dfrac{x}{8}=\dfrac{y}{3}=\dfrac{z}{10}\)

    \(\Rightarrow\dfrac{x^2}{64}=\dfrac{xy}{24}=\dfrac{yz}{30}=\dfrac{xz}{80}\)

    Apply the same sequence properties, we have:

    \(\dfrac{x^2}{64}=\dfrac{xy}{24}=\dfrac{yz}{30}=\dfrac{xz}{80}=\dfrac{xy+yz+xz}{24+30+80}=\dfrac{1206}{134}=9\)

    So \(x^2=9.64=576\)\(\Rightarrow x=24\)

    \(\dfrac{xy}{24}=9\Rightarrow xy=24.9=216\Rightarrow y=9\)

    \(\dfrac{yz}{30}=9\Rightarrow yz=270\Rightarrow z=30\)

    So \(\left(x;y;z\right)=\left(24;9;30\right)\)


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