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madhapper
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talk about dumb but i 4gotton how 2 work out area of a regular octagon can anyone show me how or give me a link to a website that tells me how. thanx
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TheWolf
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2n^2/tan(45/2)

n=length of a side
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jpowell
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http://mathworld.wolfram.com/Octagon.html
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RichE
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(Original post by madhapper)
talk about dumb but i 4gotton how 2 work out area of a regular octagon can anyone show me how or give me a link to a website that tells me how. thanx
Divide it up into 8 triangles that will each subtend 360/8 = 45 degrees at the centre.

If r is the distance from the centre to a vertex of the octagon then the area of one of these triangles is

2 x 1/2 r cos (22.5) r sin (22.5) = 1/2 r^2 sin (45)

(by thinking of it as two right-angled triangles, say).

So the total area is

4 r^2 sin (45) = 2 rt(2) r^2
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