How would I factor
I can see no other obvious way than getting two factors (ax²+bx+c)(dx²+ex+f), since if there is a complex root, there will be its conjugate as a root too. And (x-1st root)(x-conjugate) will always give an quadratic with rational coefficients.
If it's real roots, no problem.
- all roots are rational. This is not a problem, you can develop , where a,b,c,d are the roots.
- at least one root is complex (this is the most general case). This is not a problem either. We know that if the coefficients of a polynomial are rational (and thus integers), then if a complex number is a root, then its conjugate is also a root.
So divides the polynomial, that is to say this, again, is a product of a complex number and its conjugate : and
If you do the product, you'll get a quadratic (x is the variable) : (rational coefficients)
It can be deduced (with a same reasoning for the 3rd and 4th roots) that any quartic with rational coefficients can be factored into a product of 2 quadratics with rational coefficients.
Since you don't know if there are complex roots or only real roots, it's better to assume there are complex roots (real numbers are complex numbers), and thus to write the original polynomial into the product of 2 quadratics.
Is it clear ?
that's cool !Thanks Moo and o i did like that techno song lol.