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## #1 2012-10-21 23:44:53

Ronald
Guest

### Geometry

Regular polygon's area can be calculated,other polygon's area can also be calculated using graph coordinates,but i have heard that polygon's area can be calculated using sides and external angles is it true?if it is what is the method?

## #2 2012-10-22 00:42:54

bobbym

Online

### Re: Geometry

Hi;

See if you can get what you need from here:

http://www.mathwords.com/a/area_regular_polygon.htm

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #3 2012-10-22 00:59:48

Ronald
Guest

### Re: Geometry

No,i have heard that there is a formula for irregular polygon's area too(using side lengths and exterior angles

## #4 2012-10-22 01:13:20

bobbym

Online

### Re: Geometry

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #5 2012-10-22 01:19:18

zetafunc.
Guest

### Re: Geometry

If you know what the polygon looks like, you can just split it up into triangles and use Heron's formula. If you have the right angles you can then apply things like the sine rule, cosine rule, etc. to find all the sides of the triangles you have split the polygon into.

## #6 2012-10-22 01:33:05

Ronald
Guest

### Re: Geometry

The second link's 3rd method was the one I was looking for ,thank you.

## #7 2012-10-22 01:34:25

zetafunc.
Guest

### Re: Geometry

Wow, that third method is really useful. And you really do only need the side lengths and angles!

## #8 2012-10-22 01:36:17

bobbym

Online

### Re: Geometry

Hi Ronald;

You are welcome.

In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

## #9 2012-10-22 02:34:12

bob bundy
Moderator

Offline

### Re: Geometry

hi Ronald,

I like to make pictures that simplfy problems.

If you have the coordinates of the points you can always box in and make triangles and rectangles.

area of polygon = area of box less the bits you have over.  see picture for example.

Bob