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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

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: 7,524

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

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

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,781

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.****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.**

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

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: 102,781

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.****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.**

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

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)*

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

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: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

I'll try that tomorrow.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

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: 102,781

Hi MIF;

That is a neat feature.

**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.**

**Online**

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

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

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

Yes, anonimnystefy, A+

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

A winner is me -.-"

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

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: 102,781

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.****If it ain't broke, fix it until it is.**

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

Hi bobbym

Is that the shoelace formula you are using?

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,781

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.****If it ain't broke, fix it until it is.**

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

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

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

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,781

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.****If it ain't broke, fix it until it is.**

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

Plug what into a big matrix?

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,781

The coordinates.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

**Online**

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

What kind of matrix? What are the dimensions?

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,608

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: 102,781

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.****If it ain't broke, fix it until it is.**

**Online**

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

Does the same method work for complex polys?

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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