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Math Help - Help System !

  1. #1
    Junior Member
    Joined
    Dec 2009
    Posts
    46

    Help System !

    Hii !

    Can You Help Me in This System,

    Solve in \mathbb{R}^2 The System :

    \left\{\begin{array}{rcl}<br />
x^3y=9 \\ 3x + y = 6 <br />
\end{array}\right.<br />
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  2. #2
    MHF Contributor
    Joined
    Nov 2008
    From
    France
    Posts
    1,458
    Hi

    y = \frac{9}{x^3}

    3x + \frac{9}{x^3} = 6

    x^4 - 2x^3 + 3 = 0

    f(x) = x^4 - 2x^3 + 3 is decreasing over ]-oo,3/2] and increasing over [3/2,+oo[ and f(3/2) = 21/16 > 0

    Therefore f(x) > 0 for all x and there are no solutions
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