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Implict Function P3 watch

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    in edexcel p3, if they ask you to find gradient of an implicit function ( for example, x^2 +2xy+ y^2 + 16 = 0) at (3,16) or something like that, do you:

    1. find dy/dx (by using implicit differentiation) first and then stick the values right away and then rearrange to make dy/dx the subject OR

    2. rearrange FIRST and then stick the values in.

    Im not sure which to go as they will produce different answers i think.
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    (Original post by Jubba)
    in edexcel p3, if they ask you to find gradient of an implicit function ( for example, x^2 +2xy+ y^2 + 16 = 0) at (3,16) or something like that, do you:

    1. find dy/dx (by using implicit differentiation) first and then stick the values right away and then rearrange to make dy/dx the subject OR

    2. rearrange FIRST and then stick the values in.

    Im not sure which to go as they will produce different answers i think.
    You differentiate the whole expression with repsect to x and rearrange to find dy/dx and then sub the values of x and y into it.
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    They'll both give the same answer so it's a matter of preference really. If you're only finding one gradient then you may find putting values in first is easier/quicker, but if you need to find a couple, rearranging first will probably be quicker as you'll only need to rearrange once.
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    (Original post by Jubba)
    in edexcel p3, if they ask you to find gradient of an implicit function ( for example, x^2 +2xy+ y^2 + 16 = 0) at (3,16) or something like that, do you:

    1. find dy/dx (by using implicit differentiation) first and then stick the values right away and then rearrange to make dy/dx the subject OR

    2. rearrange FIRST and then stick the values in.

    Im not sure which to go as they will produce different answers i think.
    i.e.

    x^2 +2xy+ y^2 + 16 differentiates to:

    2x+2x.dy/dx+2y+2y.dy/dx = 0
    dy/dx = (-2x-2y)/(2x+2y) and sub x=3, y=16.
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    alright then, thanks 4 that.
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    I've just realised with this one if you rearrange with the symbols you get dy/dx = -1 which is independent of x or y so it's just a straight line
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    (Original post by Bezza)
    I've just realised with this one if you rearrange with the symbols you get dy/dx = -1 which is independent of x or y so it's just a straight line
    Yeah, should have seen it sooner, oh well, when's P3 again?
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    (Original post by Bhaal85)
    Yeah, should have seen it sooner, oh well, when's P3 again?
    January 2004, I got 100 :cool:
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    (Original post by Bezza)
    January 2004, I got 100 :cool:
    Fancy schmancy, show off. erm....I got an A at GCSE. lol.
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    (Original post by Bhaal85)
    Fancy schmancy, show off. erm....I got an A at GCSE. lol.
    I won't show off about my gcse maths. It was pretty good though.
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    (Original post by Bezza)
    January 2004, I got 100 :cool:
    :eek: i aim for that this time

    its on wednesday by the way
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    (Original post by kikzen)
    :eek: i aim for that this time
    You do that!!! I will be happy aslong as my exam actually achieves a grade (i.e. not a U)
 
 
 
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