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Higher Maths differentiation help watch

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    Im looking for the workings to the following differentiation question from Heinemann Higher Maths page 113 question 7a. if anyone has it

    It involves a diagram so I can't post the question.
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    Use this to do the diagram and then I'm sure someone will be able to help you.
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    I have attached a diagram of the question

    I hoep someone can help
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    (Original post by jjlang)
    I have attached a diagram of the question

    I hoep someone can help
    its just 2x*(3-x^2)
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    The notation is probably what is confusing you because you can easily get the x and X in the diagram mixed up and try to over think it.

    It would be easier to say "PQ = 2t metres" and you're wanting to show the area is 6t-2t^{3} in size.

    The length of PQ is 2t, and it is symmetric about the y axis, so the point q has an X value of t (if you were using the questions notation it would be X=x, which is just confusing!).
    Anyway, at q X=t. But q is also on the line Y = 3-X^{2}, so put in X=t to get the Y coordinate of q which is 3-t^{2}.

    Now I know the height of the rectangle, which is 3-t^{2} metres, and I know it is 2t metres long. Area is just the product of height and length so you have A = 2t \times (3-t^{2}) = 6t-2t^{3}.

    Now you can convert back into the stupid notation of the question by turning t's into x's to get A = 6x-2x^{3}.

    It is a bit of a nasty question in how it is setup.
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    Cheers for the reply mate

    Its seems a bit of a lot of work for a differentiation question and I haven't seen anything that hard in the past papers.

    I'm just glad I have the answer now.
 
 
 
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Updated: November 22, 2005

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