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Topic: Trying to find perimeter of a regular pentagon
Replies: 36   Last Post: May 31, 2013 9:26 PM

 Messages: [ Previous | Next ]
 JT Posts: 1,448 Registered: 4/7/12
Re: Trying to find perimeter of a regular pentagon
Posted: May 28, 2013 10:46 PM

On 29 Maj, 03:04, Ken Pledger <ken.pled...@vuw.ac.nz> wrote:
> In article
>
>  JT <jonas.thornv...@gmail.com> wrote:

> > On 28 Maj, 23:24, Ken Pledger <ken.pled...@vuw.ac.nz> wrote:
> > > In article <425e7c8f-10e6-428f-bcda-44e1fbf8b850@googlegroups.com>,
> > > ....
> > > 260.sin(pi/5) or 260.sin(36 degrees)....

>
> > I see your formula use Pi so i guess your formula can only calculate
> > the perimeter to the precision of the given Pi and same would go for
> > the area?

>
>    You're badly misunderstanding this.  I used pi as the radian measure
> of an angle, meaning the same thing as 180 degrees.  That's why the
> angle  pi/5  may also be written as 36 degrees.
>

> > Would it not be beneficial finding a formula using fractions, that
> > could calculate the perimeter as well as area exact, without using a
> > couple of billions of decimalpoints on Pi?

>
> > Except from being accurate it sure would put an ease to the
> > calculation machinwise or humanwise.

>
>    The formula   sin(36 degrees)  does not use the decimal expansion of
> pi,  but it's equal to  (1/4)sqrt(10 - 2.sqrt(5))  as I said.  That
> number is irrational, so its decimal expansion is a mess, and certainly
> can never be represented as a rational fraction, however much you may
> wish it.  Things like this were first studied by the Greeks around 400
> B.C.   Have you seen one of the proofs that  sqrt(2)  is irrational?
>
>       Ken Pledger.

I said a sum of fraction but a finished one, not an exact neverending
decimal expansion.

Date Subject Author
5/28/13 130bcd
5/28/13 JT
5/28/13 JT
5/28/13 Barry Schwarz
5/28/13 JT
5/28/13 JT
5/28/13 JT
5/28/13 JT
5/28/13 Ken.Pledger@vuw.ac.nz
5/28/13 JT
5/28/13 Ken.Pledger@vuw.ac.nz
5/28/13 David Bernier
5/28/13 Brian Q. Hutchings
5/28/13 JT
5/30/13 RGVickson@shaw.ca
5/31/13 Brian Q. Hutchings
5/31/13 JT
5/31/13 JT
5/31/13 JT
5/31/13 JT
5/31/13 JT
5/31/13 JT
5/31/13 Brian Q. Hutchings
5/28/13 JT
5/28/13 JT
5/28/13 Brian Q. Hutchings
5/28/13 JT
5/28/13 Brian Q. Hutchings
5/28/13 JT
5/29/13 Richard Tobin
5/29/13 JT
5/29/13 Richard Tobin
5/29/13 Brian Q. Hutchings
5/29/13 JT
5/29/13 Brian Q. Hutchings
5/30/13 Graham Cooper
5/30/13 RGVickson@shaw.ca