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C4 Implicit functions

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    Hi can someone show me where i am going wrong with these?

    Find the gradient of the stated curve at the specified point.

    2C)  3y^4 -7xy^2-12y = 5 at the point  (-2,1)

    I differentiate to get:

     12y^3\dfrac{dy}{dx} - (14xy \dfrac{dy}{dx} +7y^2) - 12 \dfrac{dy}{dx} = 0

    I get  \dfrac{dy}{dx} on its own.

     \dfrac{dy}{dx} = \dfrac{7y^2}{12y^3-14xy -12}

    I sub the values in and get  \dfrac{7}{28}, however the answer in my book says it is  \dfrac{7}{40} .
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    Nvm yh I got same as you.
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    Book's wrong.
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    I won't lie I get the same as you. Are you sure that you have the right equation and point?
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    I agree with your answer; it is 7/28= 1/4.

    Book is wrong.
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    (Original post by 0range)
    I think it should be -7y^2
    What?

    :confused:
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    (Original post by f1mad)
    What?

    :confused:
    lol nah its nothing i forgot to put a minus when doing the product rule on the -7xy^2
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    (Original post by 0range)
    Nvm yh I got same as you.

    (Original post by ghostwalker)
    Book's wrong.

    (Original post by miss katie)
    I won't lie I get the same as you. Are you sure that you have the right equation and point?
    Yeah, i doubled checked the question, i've spent over an hour on this question .
    (Original post by f1mad)
    I agree with your answer; it is 7/28= 1/4.

    Book is wrong.
    Ok thanks guys

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