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Find all rational solutions of an monic polynomial with integer coefficients


Our main tool is Corollary 2.3.

Solution: By Corollary 2.3, if $x^8-4x^5+13x^3-7x+1=0$ has a rational solution, then this rational solution must be a divisor of $1$ which means it can only be $\pm 1$.

If $x=1$, we have

$$
x^8-4x^5+13x^3-7x+1=1-4+13-7+1=4\ne 0.
$$ Hence $1$ is not a solution.

If $x=1$, we have
$$
x^8-4x^5+13x^3-7x+1=1+4-13+7+1=0.
$$ Hence $-1$ is a solution.

The only rational solution of $x^8-4x^5+13x^3-7x+1=0$ is $-1$.


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