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    1 18 hours ago Report post
    The circle (diameter 16cm) and the semicircle, including its diameter, have the same perimeter. Work out the radius, r, of the semicircle.
    So far...
    I worked out the perimeter of the circle being 16pie and I know that this would be the same as the perimeter of the semicircle.
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    Well, if the diameter is 16cm then half it for the radius..

    16/2 = 8cm.. don't they teach you that raidus is half of a circle while diameter is the full length?
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    (Original post by ckfeister)
    Well, if the diameter is 16cm then half it for the radius..

    16/2 = 8cm.. don't they teach you that raidus is half of a circle while diameter is the full length?
    yeah I know that but that's not what the question is asking... there's a circle and a semicircle with the same perimeter, which would mean their radius is different from one another
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    (Original post by neharajput)
    yeah I know that but that's not what the question is asking... there's a circle and a semicircle with the same perimeter, which would mean their radius is different from one another
    work out perimeter of circle and semicircle
    set them equal to each other solve for radius of semicircle



    so you'll whap you fraction in your calculator and you should get a right answer but i don't guarantee i will be right so Student403 and Zacken
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    Please don't post full solutions but that's not correct because you've added 16 to the pi * d / 2 instead of just d. 16 is not the diameter. d is.
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    (Original post by Student403)
    Please don't post full solutions but that's not correct because you've added 16 to the pi * d / 2 instead of just d. 16 is not the diameter. d is.
    oh yea.... lemme correct it then
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    (Original post by thefatone)
    oh yea.... lemme correct it then
    But you're still giving the full solution which is against the forum guidelines
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    (Original post by Student403)
    But you're still giving the full solution which is against the forum guidelines
    if i give a worded walkthrough of how to do it then put answer in spoiler is that ok?
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    (Original post by thefatone)
    if i give a worded walkthrough of how to do it then put answer in spoiler is that ok?
    Worded walkthrough without the answer would be appropriate
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    Moved to maths.
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    (Original post by Student403)
    Worded walkthrough without the answer would be appropriate
    I tried doing the perimeter of the semicircle= perimeter of the circle and solved it, but then it didn't work when I substituted it in, which is why I'm confused...
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    (Original post by neharajput)
    I tried doing the perimeter of the semicircle= perimeter of the circle and solved it, but then it didn't work when I substituted it in, which is why I'm confused...
    Mind showing me your workings? I can tell you where you went wrong
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    (Original post by neharajput)
    I tried doing the perimeter of the semicircle= perimeter of the circle and solved it, but then it didn't work when I substituted it in, which is why I'm confused...
    Circle: perimeter 2 \pi r = 2\pi \times 8 = 16\pi.

    Semi-circle: perimeter \frac{2 \pi r}{2} = \pi r, but including the diameter of the semi-circle gives us (perimeter plus diameter): \pi r + 2r.


    (Original post by ckfeister)
    Well, if the diameter is 16cm then half it for the radius..

    16/2 = 8cm.. don't they teach you that raidus is half of a circle while diameter is the full length?
    Bit rich coming from someone who didn't even understand the question and flopped incredibly.
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    I worked out the perimeter of the circle being 16pie



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    (Original post by Zacken)
    Circle: perimeter 2 \pi r = 2\pi \times 8 = 16\pi.

    Semi-circle: perimeter \frac{2 \pi r}{2} = \pi r, but including the diameter of the semi-circle gives us (perimeter plus diameter): \pi r + 2r.




    Bit rich coming from someone who didn't even understand the question and flopped incredibly.
    I got those formulas previously and worked it out as the radius being 5.3 recurring?
    Thank you so much for your help btw, much appreciated
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    (Original post by Student403)
    Mind showing me your workings? I can tell you where you went wrong
    Perimeter of the circle= 16pie
    (pie x radius) + (2 x radius) = 16pie
    Divide both sides by pie...
    radius + 2radius= 16
    r=16/3
    r=5.3 recurring
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    (Original post by neharajput)
    Perimeter of the circle= 16pie
    (pie x radius) + (2 x radius) = 16pie
    Divide both sides by pie...
    radius + 2radius= 16
    r=16/3
    r=5.3 recurring
    incorrect here. What happens when you divide 2radius by pi?

    It's pi btw not pie
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    (Original post by Student403)
    incorrect here. What happens when you divide 2radius by pi?

    It's pi btw not pie
    ohhh sorry loooool omg:'
    anyways...
    when you divide 2 radius by pi you get 2 radius/ pi
    but then if u multiply everything by pi to get rid of that your back to where you were before, which is what I'm unsure about...
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    (Original post by Zacken)
    Circle: perimeter 2 \pi r = 2\pi \times 8 = 16\pi.

    Semi-circle: perimeter \frac{2 \pi r}{2} = \pi r, but including the diameter of the semi-circle gives us (perimeter plus diameter): \pi r + 2r.




    Bit rich coming from someone who didn't even understand the question and flopped incredibly.
    Oh look, its that crybaby from " Improve my grades " about his lazy background thinking it was hell.
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    (Original post by neharajput)
    ohhh sorry loooool omg:'
    anyways...
    when you divide 2 radius by pi you get 2 radius/ pi
    but then if u multiply everything by pi to get rid of that your back to where you were before, which is what I'm unsure about...
    Why do you want to multiply everything by pi to get rid of it?

    We have r(2+\pi) = 16\pi \iff r = \frac{16\pi}{2+\pi}, ta-da...
 
 
 

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