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Math Help - Circle area question

  1. #1
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    Circle area question

    Want to know if there is a known formula for calculating the surface area of a circle using only the circumference as a given measurement ?
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  2. #2
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    e^(i*pi)'s Avatar
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    Since a circle is 2D it cannot have a surface area.

    However, for the area of a circle

    We know that A=\pi r^2 and C = 2 \pi r \: \rightarrow \: r = \dfrac{C}{2\pi}

    Use substitution to get a formula for A in terms of C.


    If you mean a sphere or a cylinder please reply
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  3. #3
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    We wanted to know if for example if a circle with a circumference of say 28cm would have the same area as a square whose sides are 7cm?

    Thus the perimeter measurement of each shape would be the same

    Would area be the same?
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  4. #4
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    e^(i*pi)'s Avatar
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    Ah right. The term Surface Area is largely used for the area on the surface of a 3D shape.

    I did give you the equations  A = \pi r^2 and r = \dfrac{C}{2\pi}

    Thus A = \pi \left(\dfrac{C}{2\pi}\right)^2

    You can simplify, given that there will be a pi term involved it is apparant that they won't have the same area
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  5. #5
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    What has confused us [old timers] is pi a true or precise way of finding area of circle given that creating a square from it [morphing if you like] has a different area.

    If everyday life us mere mortals have no use of pi, trigonometry and algebra. Will admit to using Pythagoras for finding squaring up a frame.

    We watching a TV show on the story of maths and has got us fascinated.
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