How many integer roots does the polynomial above have?
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When looking for integer roots, we must first determine if the polynomial is reducible over the integers. One of the well-known irreducibility criterion is the P e r r o n ′ s I r r e d u c i b i l i t y C r i t e r i o n . The criterion states that for a polynomial P ( x ) ,
P ( x ) = x n + a n − 1 x n − 1 + a n − 2 x n − 2 + . . . + a 1 x + a 0 with a 0 = 0
If ∣ a n − 1 ∣ > 1 + ∣ a n − 2 ∣ + ∣ a n − 3 ∣ + . . . + ∣ a 1 ∣ + ∣ a 0 ∣ , then P ( x ) is irreducible over the integers.
Since in the given polynomial,
∣ − 1 0 2 4 ∣ > 1 + ∣ 5 1 2 ∣ + ∣ − 2 5 6 ∣ + . . . + ∣ 8 ∣ + ∣ − 4 ∣ = 1 0 2 1
1 0 2 4 > 1 0 2 1
Then, the polynomial is irreducible over the integers, hence, it has 0 integer roots.
Useful link: Perron's Irreducibility Criterion starts on page 2 of this (It also contains the proof of this and as well as other criterion, I believe.)