Stavros Macrakis macrakis at alum.mit.edu
Wed Dec 2 04:40:38 CST 2009

```>From a mathematical point of view, some polynomials have rational
roots, or can be factored over the rationals, and some don't.  A
simpler example is

x^5-3*x-2 = (x+1)*(x^4-x^3+x^2-x-2)   real, rational root: -1

while x^5-3*x-3 doesn't factor and has one real root, but it's not
rational, and x^5-3*x-1 has three real roots, none of them rational.

You might want to look at the Wikipedia articles on polynomial
factorization and irreducible polynomials.

-s

On Wed, Dec 2, 2009 at 4:43 AM, Julien Martin <balteo at gmail.com> wrote:
> Hello,
> I have two slightly different equations :
> 4200=300*((1+r)^-1+(1+r)^-2+(1+r)^-3+(1+r)^-4+(1+r)^-5+(1+r)^-6)+4000*(1+r)^-7
> 4200=300*((1+r)^-1+(1+r)^-2+(1+r)^-3+(1+r)^-4+(1+r)^-5+(1+r)^-6)+4500*(1+r)^-7
> Notice towards the end : 4500 and 4000. That is the only difference.
> Now: from a mathematical point of view, why is the first equation not easily
> solved (some solutions are in C for example) whereas the second is easily
> solved with a simple call to the solve function?