Rational Root of $ax^3+bx+c=0$ is Product of 2 Rational Roots

In summary, a rational root is a number expressed as a ratio of two integers. To determine if a polynomial has rational roots, the rational root theorem can be used. The rational roots of a polynomial can be found using the rational root theorem and the synthetic division method. If the rational root of a polynomial is a product of two rational roots, the polynomial can be factored into two linear factors. A polynomial can have more than one rational root, with at least one additional root if it already has one.
  • #1
kaliprasad
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if for rational a,b,c $ax^3+bx+c=0$ one root is product of 2 roots then that root is rational
 
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  • #2
kaliprasad said:
if for rational a,b,c $ax^3+bx+c=0$ one root is product of 2 roots then that root is rational
my solution:
let 3 roots be $r,s,t$ and $r=st$
we have :$rst=r^2=\dfrac {-c}{a}---(1)$
$r+s+t=0,\rightarrow s+t=-r---(2)$
$rs+rt+st=r(1+s+t)=r(1-r)=r-r^2=\dfrac {b}{a}---(3)$
$\therefore r=\dfrac {b-c}{a}$ is rational
 

FAQ: Rational Root of $ax^3+bx+c=0$ is Product of 2 Rational Roots

What is a rational root?

A rational root is a number that can be expressed as a ratio of two integers, such as 1/2, -3/4, or 5/6.

How do I determine if a given polynomial has rational roots?

To determine if a polynomial has rational roots, you can use the rational root theorem. This theorem states that if a polynomial has rational roots, they will be in the form of p/q, where p is a factor of the constant term and q is a factor of the leading coefficient.

How do I find the rational roots of a polynomial?

To find the rational roots of a polynomial, you can use the rational root theorem as well as the synthetic division method. First, list all possible rational roots by taking the factors of the constant term and dividing them by the factors of the leading coefficient. Then, use synthetic division to test each root until you find one that gives a remainder of 0.

What does it mean when the rational root of a polynomial is a product of two rational roots?

If the rational root of a polynomial is a product of two rational roots, it means that the polynomial can be factored into two linear factors, each with a rational root. This can help simplify the polynomial and make it easier to solve.

Can a polynomial have more than one rational root?

Yes, a polynomial can have more than one rational root. In fact, if a polynomial has a rational root, it will have at least one more rational root. This is because if p/q is a root, then (x-p/q) will be a factor of the polynomial, and the remaining factor will have a rational root as well.

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