Rational Root Theorem

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Given a polynomial $P(x) = a_n x^n + a_{n - 1}x^{n - 1} + \ldots + a_1 x + a_0$ with integral coefficients, $a_n \neq 0$ . The Rational Root Theorem states that if $P(x)$ has a rational root $r = \pm\frac pq$ with $p, q$ relatively prime positive integers, $p$ is a divisor of $a_0$ and $q$ is a divisor of $a_n$ .

As a consequence, every rational root of a monic polynomial with integral coefficients must be integral.

The gives us a relatively quick process to find all "nice" roots of a given polynomial, since given the coefficients we have only a finite number of rational numbers to check.

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Rational Root Theorem