Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**Ronald****Guest**

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?

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,902

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

Offline

**Ronald****Guest**

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

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,902

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

Offline

**zetafunc.****Guest**

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.

**Ronald****Guest**

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

**zetafunc.****Guest**

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

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,902

Hi Ronald;

You are welcome.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

Offline

**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,525

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

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Offline