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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,552

A new app tentatively titled: Area of Polygon by Drawing

Does the title make sense? It can also double as a "solving" tool if you know enough lengths/angles.

Converting back/forth between the mouse coords (in pixels) vs graph coords (which the user can vary) kept on going wrong, but I think it is good now.

Have a play, let me know how it goes.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,469

hi MathsIsFun,

Another great page. Well done!

Haven't found any bugs yet.

Question: When adding a new point, what is your criteron for where it is placed?

And: Do I have to move my points with the mouse or is there a way to move with arrow keys or even specify a pair of coordinates exactly.

I see, for example, that your default shape is a regular pentagon. Supposing I wanted a regular hexagon?

Bob

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

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 89,046

Hi MIF;

A very good idea! I kind of like it.

I would like to have more digits.

**In mathematics, you don't understand things. You just get used to them.**

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,552

New point: half way between first 2 points.

Good suggestions. I can't figure how to implement at the moment, but will note them down.

bobbym wrote:

I would like to have more digits.

On your feet, or hands?

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 89,046

Hi MIF;

On your feet, or hands?

Hmmmm, those are fine. What would be nice is a few more digits for the area and points.

**In mathematics, you don't understand things. You just get used to them.**

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,607

I like it,but it cannot be moved left,right,up and down.

I am amazed to how many digits I was able to zoom in.

*Last edited by anonimnystefy (2012-04-21 02:39:17)*

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,552

anonimnystefy wrote:

I like it,but it cannot be moved left,right,up and down.

Click on left of drawing surface to "recenter" half way to right.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,607

I'll try that tomorrow.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,552

Added an "edit" button so you can manually change all coords. (Use refresh for latest version)

Try putting in (4,6), (2,6), (2,4), (4,4), (4,2), (6,2), (6,4), (8,4), (8,6), (6,6), (6,8), (4,8) for a positive experience.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 89,046

Hi MIF;

That is a neat feature.

**In mathematics, you don't understand things. You just get used to them.**

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,607

I am not sure what that is,but I think it is a:

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,552

Yes, anonimnystefy, A+

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,607

A winner is me -.-"

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,552

New version 0.75

Linky (same as above) Area of Polygon by Drawing

Has a "Regular" button (to make it regular, of course). A bob bundy request.

Also includes a description of the polygon: regular, concave, complex. Let me know if it gets it wrong!

Also try to make a regular polygon without using the regular button

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 89,046

Hi MIF;

Seems to be working nicely.

I use a formula involving determinants for the computation of areas. What do you use?

**In mathematics, you don't understand things. You just get used to them.**

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,607

Hi bobbym

Is that the shoelace formula you are using?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 89,046

Sorry, I can not even remember what day it is and you want me to remember what these formulas are called?

**In mathematics, you don't understand things. You just get used to them.**

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,607

Did you try searching "shoelace formula" to see if that is the one?

Btw,today is 14/5/2012,Europian date format.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
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Heck no! That is most convoluted idea I have ever seen. I just plug them into a big matrix and let M get the determinant.

**In mathematics, you don't understand things. You just get used to them.**

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
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Plug what into a big matrix?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 89,046

The coordinates.

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
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What kind of matrix? What are the dimensions?

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**MathsIsFun****Administrator**- Registered: 2005-01-21
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bobbym wrote:

I use a formula involving determinants for the computation of areas. What do you use?

Same, really. Sum up (pt0.x * pt1.y - pt0.y * pt1.x) for successive pairs of points (including last to first). Need to divide by 2 at end.

Couldn't work out how to get area for complex shapes, though, so just say "complex".

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 89,046

Sorry, I seemed to have dropped the determinant way in favor of some algorithm. This is the one I have in my notes right now. I was wondering what MIF is using

**In mathematics, you don't understand things. You just get used to them.**

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,607

Does the same method work for complex polys?

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