# Re: "frac2" button

```I hear roumers of ppl working on a symbolic manipulation for the ti-86!
does anyone have any further info on how or where i can get this
invofmatin?

Tavis Segura <tsegura@rice.edu> wrote in article
<34CD5CB0.1C4C@rice.edu>...
> First of all, the TI-92 does symbolic math, but once you approximate
> your numbers, you are not much better off than you are on the '85.  The
> "exact()" command is not foolproof: do divination there.  Take a look.
> The function
>
> approx(sqrt(2)/2)
>
> will return .70710678118655 for an answer.  In that case,
>
> exact(.70710678118655)
>
> would return sqrt(2)/2, wouldn't it?  Not a chance.  All it gives you is
> a large fraction:
>
> 14142135623731
> --------------
> 20000000000000
>
> errors) does not do any better:
>
> exact(.70710678118655,1*10^-13)
>
>  =   2744210
>      -------
>      3880899
>
> In short, The TI-92 cannot do this "frac2" stuff.  It is a truly amazing
> machine, but don't expect too many miracles.  (Sigh) I guess you have to
> figure out the numbers yourself (like multiplying by sqrt(2) in this
> example to get approximately 1.) or using better judgement about what
> you want your calculator to approximate.
>
> Tavis
>
> Chopps wrote:
> >
> > then how do you explain how the ti-92 does it?  I want some kind of
> > symbolic manipulation, that i hear ppl are working on!!!
> >
> > RWW Taylor <RWTNTS@RITVAX.ISC.RIT.EDU> wrote in article
> > <01ISU8F74CAUCIRDY1@ritvax.isc.rit.edu>...
> >
> >
> > > As soon as you can input a decimal that is _exactly_ equal to half
> > > the square root of 3, then you can start thinking about how to create

> > > a "frac2" button that will report this.  But that will be a very long
> > > time!
> > >
> > > The best you can possibly do is make a _guess_ or a _bet_ that the
> > > decimal value in your hands was really meant to be an approximation
> > > of some particular easily-described irrational value.  If you have
> > > some 12- or 13-place representation stored in memory W, for example,
> > > you might try using Frac on W^2 and decide whether you like what you
> > > see.  Another plausible effort might be to divide W by pi (and try
> > > Frac again, maybe).  Of course, what you have might just be a
> > > representation of 2 minus the square root of 3, or the
> > > cube root of 5 plus the cube root of 7, or pi^2, or some weirder
> > > number that you will never guess the secret of.  Calculators are
> > > wonderful, but they have no supernatural powers of divination (as far
> > > as I know, anyway).  :-)}
> > >
>

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