Math Is Fun Forum

CIV

Member

Registered: 2014-11-09

Posts: 74

Need help factoring this polynomial...

It's late and my brain is tired, but darn. This is the polynomial:

I know how to find possible factors:

So the possibilities are:

But none of them are factors! I used my graphing calculator and it calculated a zero at about 2.5, which is 5/2. The calc is telling me 2.4448652, but the y value isn't exactly zero though. Whatever. I solved the equation using 5/2 and it doesn't solve to zero. Please help me understand this.

Last edited by CIV (2015-09-10 19:39:38)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Need help factoring this polynomial...

Hi;

The rational root theorem only provides a possible list of rational roots of a polynomial. They do not have to be roots of the equation. 5 / 2 is not a root of that equation so it will not work as you found it.

There are other methods to locate and isolate the roots.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

CIV

Member

Registered: 2014-11-09

Posts: 74

Re: Need help factoring this polynomial...

Hi;

The rational root theorem only provides a possible list of rational roots of a polynomial. They do not have to be roots of the equation. 5 / 2 is not a root of that equation so it will not work as you found it.

There are other methods to locate and isolate the roots.

OK. Thanks. I haven't been taught how to solve higher degree polynomials yet, other than the rational roots theorem, so I will not go here just yet. Don't want to veer of course. The problem I was solving didn't ask me to factor this polynomial. This polynomial is the numerator of a rational equation. I was asked to determine the domain, horizontal asymptote, and the vertical asymptote. I kind of veered of course with trying to factor it.

Thanks.