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    I need help please on question 15)d)
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    (Original post by otrivine)
    I need help please on question 15)d)
    What have you done so far? I'd start by finding the area of the right-angled triangle you've drawn on the figure and subtract from it the area under the curve.
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    (Original post by davros)
    What have you done so far? I'd start by finding the area of the right-angled triangle you've drawn on the figure and subtract from it the area under the curve.
    I integrated 4sinx which is -4cosx+c ? assume x is detha,

    But I dont get the limits?
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    (Original post by otrivine)
    I need help please on question 15)d)
    Firstly, it's unclear from the diagram but I think that the required area is just the lower bit that looks like a triangle - not the upper bit with the ink lines on.
    There's a neat way and a hackish way. You can find y in terms of x, by finding theta in terms of x and substituting. Alternatively, and much nicer, you can use the formula:
    \displaystyle \int y dx = \int y \frac{dx}{d \theta} d\theta.
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    (Original post by Smaug123)
    Firstly, it's unclear from the diagram but I think that the required area is just the lower bit that looks like a triangle - not the upper bit with the ink lines on.
    There's a neat way and a hackish way. You can find y in terms of x, by finding theta in terms of x and substituting. Alternatively, and much nicer, you can use the formula:
    \displaystyle \int y dx = \int y \frac{dx}{d \theta} d\theta.
    No I used the area formula
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    (Original post by otrivine)
    No I used the area formula
    Ah, if there's a formula that spits out what you need then feel free to ignore me
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    (Original post by Smaug123)
    Ah, if there's a formula that spits out what you need then feel free to ignore me
    But dont get how they did the limit?
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    (Original post by otrivine)
    No I used the area formula
    What area formula

    Smaug is correct

    You found the limits when you found the co-ordinates of P and R
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    Why don't you create a triangle with the first quadrant inside it. Then you can take away the area of the triangle away from the area of the curve from the triangle.
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    (Original post by TenOfThem)
    What area formula

    Smaug is correct

    You found the limits when you found the co-ordinates of P and R
    Because to find the area for intgration , you integrate y with the limits
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    (Original post by otrivine)
    Because to find the area for intgration , you integrate y with the limits
    Yes, as Smaug said
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    (Original post by TenOfThem)
    Yes, as Smaug said
    and so you integrate only 4sinx
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    (Original post by otrivine)
    Because to find the area for intgration , you integrate y with the limits
    You integrate y(x) with respect to the x-limits. If you integrate with respect to a parameter then you must ensure that your limits are the appropriate values of the parameter.
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    (Original post by otrivine)
    Because to find the area for intgration , you integrate y with the limits
    Can you give us the expression you're integrating, so we know what you mean by "area formula"? Then we might be able to help with the limits…
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    (Original post by otrivine)
    and so you integrate only 4sinx
    You need to integrate y with respect to x

    but y = 2Sin(theta) so you need to do what Smaug said to do
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    this is what I mean?
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    (Original post by otrivine)
    this is what I mean?
    The limits are the theta limits, and you need to rewrite your dx in terms of d(theta) as smaug showed you earlier.
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    (Original post by otrivine)
    this is what I mean?
    That is incorrect

    You can not integrate Sin(theta) with respect to x

    You need to use the formula that Smaug showed you



    The limits are

    x/theta at point P
    x/theta when y=0
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    (Original post by otrivine)
    this is what I mean?
    You haven't actually integrated correctly. You've integrated d(theta) instead of d(x).
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    (Original post by Smaug123)
    You haven't actually integrated correctly. You've integrated d(theta) instead of d(x).
    ok

    what would you integrate then can you show me
 
 
 
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