MikesWagon

I'm a right lazy sod today, need to calculate the area of shapes such as a circle, donut & octagon, but it's many moons ago since I was at school.

Could somebody please tell me the formulaes for the above shapes, or point me to somewhere I can find this out.

Cheers,

Mike.

MarkO

Area of a circle is (pi x r)squared.

Can't remember the others.

Boost II

iTrader: (1)

Isn't it pi x (r squared) for a circle.

Triangle is 1/2 base x height

Dougnut you need to subtract one circle from the other.
Think of an octagon as being made up of 8 triangles etc

fast bloke

octagon is something like 4.8 times length of one side squared

fast bloke

Donut is a bit complicated - It is the circumference of the torus through the centre of the cylinder multiplied by the circumference of the cylinder if you think of the torus as being a cylinder bent into a circle. The formula is 4b(a−b)pi squared where a is the radius of the entire torus, and b is the radius of the cylinder. Does that make any sense?

[Edited by fast bloke - 6/6/2002 3:59:05 PM]

carpet

surely you just work out the area of the big circle and then the area of the small circle and subtract them !!! all that 4b - a ..... seems a lot of pissin about if you ask me !

fast bloke

OK - so give us a formula for that carpet ?

MikesWagon

Knew how to get the donut - mmmmmm donuts! - just needed the circle to get me started on that one.

Octagon's still a funny, all I've got is the mm across the flats. I know I could calculate the area of a triangle 1/16th of the octagon, but there must be a slicker way surely.

Anybody got a slide rule? Won't help, but I've got an itch I can't reach

Mike.

HHxx

Octagon = 8 * ((0.5 * L) * N)

L = length of a side
N = distance from centre of side to centre of the octagon

H

Katana

Area of circle is pi * d^2/4.

Okay, okay, its also pi r^2. :P

fast bloke

Mike - after 4 pages of trying to do it the hard way it simplifies into 4.828 times the length of a side (probably the measurement you have) squared.

dsmith

And for the octagaon if I'm not mistaken,

N = SqRt((L^2)/2) + L/2

But could be wrong of course.....

Deano

carl

fast bloke's donut is a 3-d one (a torus). I think Mike's one is properly called an annulus (no smirking at the back there)

MattN

does it have gold wheels?