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Math Help - Circumference help!

  1. #1
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    Circumference help!

    Hey, just a quick question
    do you know how to find the circumference of a circle by using the diameter
    do if the diameter is 12.3cm what would it be and how would you work it out ?
    thanks
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  2. #2
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    The formula for circumference C of a circle with diameter d is C = \pi{d}.
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  3. #3
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    could you explain more please
    so it would be ...c= pie x 12.3
    ??
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  4. #4
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    Quote Originally Posted by Louismoore16 View Post
    could you explain more please
    so it would be ...c= pie x 12.3
    ??
    Yes, that is correct.
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  5. #5
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    right so would the answer for c=piex12.3= 38.6

    and how do i work out the area of a circle using the diameter??
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  6. #6
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    Your answer is correct.

    The area A of a circle with radius r is A = \pi{r^2}. Since r is half of d, the formula could be written as A = \pi{(0.5d)^2} = 0.25\pi{d^2}.
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  7. #7
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    Quote Originally Posted by Louismoore16 View Post
    right so would the answer for c=piex12.3= 38.6

    and how do i work out the area of a circle using the diameter??
    That would be correct to the nearest tenth. And, it's "pi" not "pie".

    I like pie. But, did you know that in Alaska, pi has only a value of 3. I suppose the cold shrinks everything. They call it "Exkimo Pi". Just kidding!
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  8. #8
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    right so just let me check to see if this is right, if it is im sorted
    the question was find the area of a circle using diameter=14.8cm
    so i do 14.8 divided by 2=7.4 then pie x 7.4squared=172.3
    is this right?
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  9. #9
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    Looks good to me, again assuming that you are rounding to the nearest tenth.
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