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Thread: Please help with the fff questions

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    Please help with the fff questions

    1) d/dx loge 2x/x+1

    2) if l=w=x and h=y of a rectangular prism I worked out the volume to be V=(125x-x^3)/2. Find the dimensions for the maximum volume.

    3) for the curve y=x^2-x-2.
    a) Explain why the area bounded by the curve, the x axis and the lines x=1 and x=3 is not given by the integral with bounds 3 and 1 (x^2-x-2)dx.
    b) Find the area bounded by the curve the x axis and the lines x=1 and x=3.

    4) Find the point on the curve y= 3 +4x-x^2 where the tangent is perpendicular to y=x/3+1

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    Re: Please help with the fff questions




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    Re: Please help with the fff questions

    Sorry for bad writing v_v

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    Re: Please help with the fff questions

    Quote Originally Posted by HeroWise View Post


    For question two the shape is a rectangular prism what will the height be if h= 125/2x-x/2?

    I still don’t get Q3. The question says you can not use 1 and 3 as the bounds to calculate the area and yet you did
    Last edited by kpad5991; 17 Mar 2018 at 7:51 PM.

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    Re: Please help with the fff questions

    Here are the questions can you do the one with the stars please (questions listed below). Maybe seeing the questions might make it clearer.
    Q11 b ii
    Q11 c ii, iii
    Q12 a and b

    https://imgur.com/gallery/G4TwR

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    Re: Please help with the fff questions

    OOHHH
    Ok see in q3, if u see its graph, a section is below the x axis, thus getting subtracted from the portion which is above the x axis:


    A1 and A2 are the two areas we are tryna find but A1 is belo the axis, it WILL get subtracted when we integrate from 3 to 1
    If u notice just after the integration step I have


    (-3/2)-(1/3-1/2-2)

    The (-3/2) is later absolute valued to give (3/2), i just removed the negative sign, if it were to stay it would subtract the original area and anyway u cant have neg area
    Yeah sure ill do em rn

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    Re: Please help with the fff questions




    Doing the last one now

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    Re: Please help with the fff questions

    Thank you so much for this. You are awesome

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    Re: Please help with the fff questions

    Your awesome too !

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    Re: Please help with the fff questions

    And here is the last questions answer:



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    Re: Please help with the fff questions

    Thank you so much. Okay last two part b and d

    https://imgur.com/gallery/9h7mn

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    Re: Please help with the fff questions

    b)

    i) use the arc length formula to find and .

    ii) use the area formula to find the areas of the large sector and the small sector .

    For d), be careful when notating angles using one letter () - it's technically ambiguous since that could be referring to any of two angles.

    iii) and are corresponding sides of the two similar triangles. So to find their ratio you only need to find the ratio of any other two corresponding sides of the triangles, e.g. and .
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    Re: Please help with the fff questions



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    Re: Please help with the fff questions

    for first step in the formula, i tend to derive it and not memorise it cos idk i cant get to stick it in my head, like l=rtheta, htats simple but my assurance increases if I derive it haha

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    Re: Please help with the fff questions

    Quote Originally Posted by HeroWise View Post
    OOHHH
    Ok see in q3, if u see its graph, a section is below the x axis, thus getting subtracted from the portion which is above the x axis:


    A1 and A2 are the two areas we are tryna find but A1 is belo the axis, it WILL get subtracted when we integrate from 3 to 1
    If u notice just after the integration step I have


    (-3/2)-(1/3-1/2-2)

    The (-3/2) is later absolute valued to give (3/2), i just removed the negative sign, if it were to stay it would subtract the original area and anyway u cant have neg area
    Yeah sure ill do em rn
    So why is this wrong??? Why can’t you work out the area seperately and add them???

    https://imgur.com/gallery/P2Kou

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    Re: Please help with the fff questions

    You can, but writing



    is a little questionable, and some markers may penalise you for this.

    Alternatively you could take the absolute value



    or even swap the bounds of integration

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    Re: Please help with the fff questions

    But then our areas are different? Cause wouldn’t you have to take both areas A1 and A2 get the absolute values and add them. For A1 I get 7/6 and A2= 11/6 so the total is 3 u^2. Your area was a fraction

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    Re: Please help with the fff questions

    My area was a fraction because we still need to add the other area, the one under the curve from 3 to 2.

    Technically you only need to take the absolute value of

    since the other part is known to be positive.

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    Re: Please help with the fff questions

    ofc u can integrate them separately, thats what you are meant to do, BUt if u do it in a step you need to abs the value which gives -ve

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    Re: Please help with the fff questions

    So 3u^2 is correct?

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    Re: Please help with the fff questions



    Ja senpai

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