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Thread: I just had one class of differential equations and a huge homework about it

  1. #1
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    Exclamation I just had one class of differential equations and a huge homework about it

    IF dy/dx= squareroot(x/y) and y=4 then x=1, what is the equation y?
    Last edited by emilyastrid; Jul 30th 2018 at 09:22 AM.
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  2. #2
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    Re: I just had one class of differential equations and a huge homework about it

    Quote Originally Posted by emilyastrid View Post
    IF dy/dx= squareroot(x/y) and y=4 then x=1, y =???
    You just told us that $y=4$. Now you want to know what y is equal to? It is still 4.
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    Re: I just had one class of differential equations and a huge homework about it

    i meant the equation y.
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    Re: I just had one class of differential equations and a huge homework about it

    Quote Originally Posted by emilyastrid View Post
    i meant the equation y.
    You have

    $$\dfrac{dy}{dx} = \sqrt{\dfrac{x}{y}}$$

    Multiplying out gives:

    $$\sqrt{y}dy = \sqrt{x}dx$$

    You can rewrite as:

    $$y^{1/2}dy = x^{1/2}dx$$

    Now, integrate both sides. Plug in $(1,4)$ to determine the constant of integration. Solve for $y$.
    Thanks from emilyastrid and topsquark
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    Re: I just had one class of differential equations and a huge homework about it

    Quote Originally Posted by emilyastrid View Post
    IF dy/dx= squareroot(x/y) and y=4 then x=1, what is the equation y?
    You have a typo- you meant to say "y= 4 when x= 1" or, more simply, "y(1)= 4".
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