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Math Help - Parametric Equations

  1. #1
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    Parametric Equations

    Hi all, first time poster but if this goes well will probably be seeking out more help.

    So we are doing parametric equations and I understand how to find the slope, however from their I'm totally lost. >.<


    Please don't just answer, I have an exam soon and if you could explain why, it would be wonderful.


    The original question is:
    Find an equation of the tangent line to this curve

    x=(t^2)-8t
    y=(t^2)+7t


    So I know you take the derivative of both sides to find dx/dt and dy/dt

    dx/dt=2t-8
    dy/dt=2t+7

    So the slope is equal to...

    (2t+7)/(2t-8)


    The T value they give is 8/2 (4?)

    So..

    2(4)+7/2(4)-8
    15/0

    Slope is undefined....


    From there I have no idea

    _______________________



    However if the slope were to work, such as with this equation...

    x=(t^3)-3t
    y=t^2
    @ t= 3

    I get the slope 1/4

    so
    y=(x/4)+b

    However, I don't know what values to put for x and y!!



    Anyway. Thank you for any help.
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  2. #2
    MHF Contributor Unknown008's Avatar
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    Quote Originally Posted by Khart View Post
    However if the slope were to work, such as with this equation...

    x=(t^3)-3t
    y=t^2
    @ t= 3

    I get the slope 1/4

    so
    y=(x/4)+b

    However, I don't know what values to put for x and y!!



    Anyway. Thank you for any help.
    Put t = 3 in the parametric equation to get the value(s) of x and y.

    x=(3^3)-3(3)
    y=(3)^2
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  3. #3
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    You need to post the whole problem using the exact wording.
    I find it hard to follow your question.
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  4. #4
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    That is the whole problem =o

    Its an online assignment so the descriptions are a bit low.
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  5. #5
    MHF Contributor Unknown008's Avatar
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    Well, the value of T they gave is strange... how did they gave the problem question?
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  6. #6
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    If you mean that there is a text box with "8/2" for t then I would be inclined to guess that they are giving you two problems and asking for the tangent line at both t= 8 and t= 2.
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  7. #7
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    I know its strange! Its Wiley Plus which is honestly the worst online homework in the world.

    I wrote it down word for word.
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  8. #8
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    earboth's Avatar
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    Quote Originally Posted by Khart View Post
    Hi all, ...
    ...
    The original question is:
    Find an equation of the tangent line to this curve

    x=(t^2)-8t
    y=(t^2)+7t


    So I know you take the derivative of both sides to find dx/dt and dy/dt

    dx/dt=2t-8
    dy/dt=2t+7

    So the slope is equal to...

    (2t+7)/(2t-8)


    The T value they give is 8/2 (4?)

    So..

    2(4)+7/2(4)-8
    15/0

    Slope is undefined....


    From there I have no idea

    ...
    All your calculations and considerations are OK!

    1. Calculate the coordinates of the tangent point T(x_T, y_T).

    2. If the slope is undefined then the equation of the tangent is x = x_T
    Attached Thumbnails Attached Thumbnails Parametric Equations-tang_anparametric.png  
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