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Math Help - Differentiation: Find the coordinates where..

  1. #1
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    Differentiation: Find the coordinates where..

    Find the coordinates where the gradient of the tangent to y = 2x^2 - 5x + 2:
    a) is parallel to the line 1 - 3x.
    b) equal to the gradient of the function g(x) = 1/3x^3 - x^2 for the same value(s) of x.

    I've been trying to figure it out by doing 1 - 3x = dy/dx but I can't get what the answer says and as for b, I just don't get it at all..

    Please help and show working! Thanks a lot.
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  2. #2
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    You don't want to set the gradient of one equal to the other, you want to set the gradient of one equal to the gradient of the other.

    For a) the gradient of the other is -3 everywhere, whereas for b) you'll solve a quadratic to see where the two gradient functions (i.e. dy/dx and d g(x) / dx ) have the same value.
    Last edited by tom@ballooncalculus; September 16th 2010 at 03:09 AM.
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  3. #3
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    Thanks. Got it correct.
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