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Math Help - Circle's Diameter

  1. #1
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    Circle's Diameter

    If the circumference of a circle is doubled, the diameter of the circle

    (1) remains the same
    (2) increases by 2
    (3) is multiplied by 4
    (4) is doubled
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  2. #2
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    Quote Originally Posted by symmetry View Post
    If the circumference of a circle is doubled, the diameter of the circle

    (1) remains the same
    (2) increases by 2
    (3) is multiplied by 4
    (4) is doubled
    Is doubled.

    C=\pi d
    Thus,
    2C=\pi (2d)
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  3. #3
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    ok

    If the circumference of a circle is 12, the the diameter = pi(12)(d), right?

    What whatever the circumference equals, the diameter increases by the same amount, right?
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  4. #4
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    Quote Originally Posted by symmetry View Post
    If the circumference of a circle is 12, the the diameter = pi(12)(d), right?

    What whatever the circumference equals, the diameter increases by the same amount, right?
    Right
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  5. #5
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    Quote Originally Posted by symmetry View Post
    If the circumference of a circle is 12, the the diameter = pi(12)(d), right?...
    Hello,

    you know already that the circumference of a circle is calculated by:

    c=2 \cdot \pi \cdot r= \pi \cdot d, with diameter = 2 * radius.

    Plug in the value you know:

    12= \pi \cdot d \Longleftrightarrow d=\frac{12}{\pi}.

    In general:

    c=\pi \cdot d \Longrightarrow d=\frac{12}{\pi} \Longrightarrow \pi=\frac{c}{d}

    EB

    PS: I've attached a diagram which helps to memorize the right formula: Cover the variable you want to calculate with your fingertip. The remaining term shows how to calculate the covered value.
    Attached Thumbnails Attached Thumbnails Circle's Diameter-umkrs_forml.gif  
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  6. #6
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    ok

    Thank you for the notes and reply.

    Earboth,

    Thank you for the picture. I think tutors should use pictures here to help students.
    Last edited by ThePerfectHacker; January 18th 2007 at 01:21 PM.
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