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# The Fencing Problem - semi-circles watch

1. Can anyone tell me if it is possible to work out how the fencing would have to be distributed to make a semi-circle (ie. how long the curved edge would be, and how long the straight edge would be)
Can anyone tell me if it is possible to work out how the fencing would have to be distributed to make a semi-circle (ie. how long the curved edge would be, and how long the straight edge would be)
The curved bit would have to be pi/2 times the length of the straight bit.

Ben
3. (Original post by Ben.S.)
The curved bit would have to be pi/2 times the length of the straight bit.

Ben
So in other words, with 1000 metres of fence, it would be 1000/(pi/2) to work out the length of the straight? Or does what I just said make no sense?
4. If you mean the perimeter of a semicircle:

P=((pi)d/2)+d, where d=diameter
5. So how would I work out the diameter from the perimeter?
So in other words, with 1000 metres of fence, it would be 1000/(pi/2) to work out the length of the straight? Or does what I just said make no sense?
The whole fence must be of length x[1+(pi/2)]. You can find the lengths of either part of a semicircle from that. So, with a 1000m fence;

x = 1000/[1+(pi/2)]
Straight length = x
Curved length = (pi/2)x

Ben
7. (Original post by XTinaA)
If you mean the perimeter of a semicircle:

P=((pi)d/2)+d, where d=diameter
To get d:

P=((pi)d/2)+d
=d((pi)/2+1)
d=P/(pi/2+1) (edited error, cheers Ben S)

I think...
8. Thanks, I got the grasp of it (eventually) from what Ben said.
9. By the way, you're wonderful, wonderful people.
10. (Original post by XTinaA)
To get d:

P=((pi)d/2)+d
=d((pi)/2+1)
d=(pi/2+1)/P

I think...
You've got your division the wrong way round!

Ben
11. (Original post by Ben.S.)
You've got your division the wrong way round!

Ben
Guuh! Oh yeah. Youse know what I mean...
12. Doesn't matter, you still know what you're talking about better than I do.

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Updated: March 3, 2004
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