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Math Help - Slope Fields

  1. #1
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    Slope Fields

    Differential Equation dy/dx= 1/y: describe properties of this equation and their effect on the slope field that represents the family of solutions to this DE
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    Re: Slope Fields

    What do the isoclines for this direction field look like?
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    Re: Slope Fields

    i don't know that word ha im sorry
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    Re: Slope Fields

    An isocline is the locus of points in the plane such that the slope is always the same. For example, where is the slope always 1?
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    Re: Slope Fields

    when y=1?
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    Re: Slope Fields

    Exactly! How about where the slope is always k, where k is an arbitrary constant?
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    Re: Slope Fields

    when y=0?
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    Re: Slope Fields

    No. How did you find the slope is always 1 along the line y = 1?
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    Re: Slope Fields

    because 1/1 is 1
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  10. #10
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    Re: Slope Fields

    Right. We could state:

    \frac{dy}{dx}=\frac{1}{y}=1\,\therefore\,y=1

    So, if we generalize, we can state:

    \frac{dy}{dx}=\frac{1}{y}=k\,\therefore\,y=\frac{1  }{k}

    The whole point to this is that we find the isoclines are horizontal lines, and to find the isocline where the slope is k, we use the line y=\frac{1}{k}. Finding isoclines is a method to make sketching the direction field easier.

    What kind of symmetry do we observe in the direction field?
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  11. #11
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    Re: Slope Fields

    the higher y is, the smaller the slope
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    MHF Contributor MarkFL's Avatar
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    Re: Slope Fields

    Yes, that's true for positive y. For negative y, the opposite is true. The further we get from the x-axis, the smaller the magnitude of the slope is.

    The symmetry I am speaking of comes from y'(-y)=-y'(y). So, what kind of symmetry can we expect to find in the solution space?
    Last edited by MarkFL; December 9th 2012 at 11:02 PM.
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  13. #13
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    Re: Slope Fields

    isn't it the same thing? or are you supposed to take the antiderivative of 1/y?
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    Re: Slope Fields

    You can solve the ODE by integration, but for this exercise you are expected to merely look at the nature of the solution from the direction field.

    By looking at the direction field, we can see that the solutions will be symmetric across (or reflected about) the x-axis.
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  15. #15
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    Re: Slope Fields

    how can we draw a solution curve through (-1,0) if that point doesnt exist?
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