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surface area of revolution - cartesian form watch

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    How does one find the surface area of revolution for a cartesian equation? The Edexcel booklet only give you it for parametric form.

    Also, how do you find the area of a sector from a cartesian equation?
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    (Original post by lesser weevil)
    How does one find the surface area of revolution for a cartesian equation? The Edexcel booklet only give you it for parametric form.
    Surface area due to rotation about x axis:2pi∫y[1+(dy/dx)^2]^0.5 dx with limits xA and xB.
    Surface area due to rotation about y axis: 2pi∫x[1+(dx/dy)^2]^0.5 dy with limits yA and yB

    Also, how do you find the area of a sector from a cartesian equation?
    What sort of a sector?
    I'm sure you know the area bounded by the curve and the x axis is ∫y dx with limits xA and xB.
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    (Original post by Gaz031)

    What sort of a sector?
    I'm sure you know the area bounded by the curve and the x axis is ∫y dx with limits xA and xB.
    Ah yeah, slight slip of the memory there... **blush**
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    (Original post by lesser weevil)
    Ah yeah, slight slip of the memory there... **blush**
    It happens. I occasionally find it worrying that I remember the formula for the radius of curvature in parametric form and results such as ∫1/√(x²+a²) dx better than I know the result for the sum of a geometric series
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    (Original post by Gaz031)
    It happens. I occasionally find it worrying that I remember the formula for the radius of curvature in parametric form and results such as ∫1/√(x²+a²) dx better than I know the result for the sum of a geometric series
    nice skill - i used to have photographic memory at GCSE's but become lazy and i cant even remember teh standard form for partial fractions any more!!!! but i can remember quite a few digits of pi

    pk
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    (Original post by Gaz031)
    It happens. I occasionally find it worrying that I remember the formula for the radius of curvature in parametric form and results such as ∫1/√(x²+a²) dx better than I know the result for the sum of a geometric series
    ooh, are we meant to know the sum of geometric series for P5....? :eek:
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    nice skill - i used to have photographic memory at GCSE's but become lazy and i cant even remember teh standard form for partial fractions any more!!!! but i can remember quite a few digits of pi
    Lol. I know pi=3.14..... and e=2.718... and that's about it for remembering constants. With a lot of the results (eg all the trig formulae) it's easy to derive them and you only need some main results.

    ooh, are we meant to know the sum of geometric series for P5....?
    You need to know everything that has come before P5 in addition to the new content. It's doubtful that it will come up though.
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    (Original post by Gaz031)
    You need to know everything that has come before P5 in addition to the new content. It's doubtful that it will come up though.
    Ouch, hold me up someone!!!!!!!!!!
    oooooooooooooooooooooooooooooooo ooo barf.
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    (Original post by lesser weevil)
    Ouch, hold me up someone!!!!!!!!!!
    oooooooooooooooooooooooooooooooo ooo barf.
    Don't worry, a lot of it is in the formula book and as you've used it before you only need the results. Also they wont set hard questions based solely on previous content.
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    (Original post by Gaz031)
    Don't worry, a lot of it is in the formula book and as you've used it before you only need the results. Also they wont set hard questions based solely on previous content.
    yeah, the first time I read the formula booklet it made me SOOO happy... hehe!
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    (Original post by lesser weevil)
    yeah, the first time I read the formula booklet it made me SOOO happy... hehe!
    but be careful with the questions about conics ... they are really nasty ... with tangent and normal.
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    (Original post by BCHL85)
    but be careful with the questions about conics ... they are really nasty ... with tangent and normal.
    what's a conic?

    If you have an equation with a point and have to find the tangent to it or the normal to it, it aint that hard.
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    (Original post by lesser weevil)
    what's a conic?

    If you have an equation with a point and have to find the tangent to it or the normal to it, it aint that hard.
    plane on a cone when you cut it in various ways
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    (Original post by BCHL85)
    but be careful with the questions about conics ... they are really nasty ... with tangent and normal.
    not that bad - only when the examiners are feeling nasty, otherwise its easy - but it is the only think i seem to be losing marks on in P5 cos when they ask to work out angles and conics stuff, it can get messy and confusing
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    (Original post by Phil23)
    not that bad - only when the examiners are feeling nasty, otherwise its easy - but it is the only think i seem to be losing marks on in P5 cos when they ask to work out angles and conics stuff, it can get messy and confusing
    I agree that sometimes it can get a bit messy and the key really is to keep things tidy and logical. If it's a large and lengthly question where it gives you quite a lot of information try to break it into small parts and decide how you can use each piece of information.
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    (Original post by Gaz031)
    I agree that sometimes it can get a bit messy and the key really is to keep things tidy and logical. If it's a large and lengthly question where it gives you quite a lot of information try to break it into small parts and decide how you can use each piece of information.
    And always draw a diagram!
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    Do we need to know about polar coordinates for P5?
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    (Original post by lgs98jonee)
    Do we need to know about polar coordinates for P5?
    thats basically in P4, but as stated earlier..we need to know everything in pure from P1 upto P5 for the exam
    and again..nothing major should come up on that really
    they have enough to test on for P5! :rolleyes:
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    is P5 the hardest of the P4 - 6 exams?
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    (Original post by lesser weevil)
    is P5 the hardest of the P4 - 6 exams?
    middle - p6 is hardest in my opinion
 
 
 
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