# area of octagonWatch

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#1
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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14 years ago
#2
2n^2/tan(45/2)

n=length of a side
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14 years ago
#3
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14 years ago
#4
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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