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Math Help - normal line

  1. #1
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    normal line

    An equation of the line normal to the graph of y = (3x^2 + 2x)^.5 at (2,4) is

    a) -4x + y =20
    b) 4x + 7y = 20
    c) -7x + 4y = 2
    d) 7x + 4y = 30
    e) 4x + 7x = 36


    so i know you have to get the derivative, which I found to be (3x+1) / (sqrt[3x+2])

    but now what do i do
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  2. #2
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    Find the derivative of your function. Use x=2 to find the slope,m, at that point.

    The normal will be the perpendicular, so it's slope will be the negative reciprocal of the slope you found. Then, use your given points (2,4) and y=mx+b to find your normal line equation. It is one of your options. I see it there. Remember, the options are in standard form.
    Last edited by galactus; November 24th 2008 at 05:38 AM.
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  3. #3
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    thank you.

    did you get (E) as the final ans?
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  4. #4
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    Yep
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