B.I1. Prove that 30x - 91 (where ne Z,n>1) has no roots in Q. 12. Let Fbea field and f(x) F[X]. If'e E Fand f(x +) is imreducible in Flx), prove that /(x) is irreducible in Flx). [Hont: Prove the contrapositive.] 13. Prove that f(x) -+ 4x + L is irreducible in Olxl by using Eisenstein's

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Certainly! Below is the transcribed text formatted as if it were to appear on an educational website.

---

## Exercises on Polynomials and Irreducibility

1. Prove that the polynomial \(x^2 + x + 1\) has no roots in any field of characteristic 3.

2. Show details of the proof that if a monic polynomial with integer coefficients has a root in \(\mathbb{Q}\), then this root must be an integer.

3. If a monic polynomial with integer coefficients has a root in \(\mathbb{Q}\), show that this root must be an integer. 

4. Demonstrate how each polynomial is irreducible in \(\mathbb{Q}[x]\), as seen in Example 3.
   - \(x^4 + 2x^2 + x + 1\)
   - \(x^4 + x^3 + x^2 + x + 1\)

5. Use Eisenstein's Criterion to show that each polynomial is irreducible in \(\mathbb{Q}[x]\):
   - \(x^4 - 4x + 22\)
   - \(5x^4 - 6x^3 + 36x - 6\)

6. Demonstrate that there are infinitely many integers \(k\) such that \(x^4 + 12x^2 - 21x + k\) is irreducible in \(\mathbb{Q}[x]\).

7. Show that each polynomial is irreducible in \(\mathbb{Z}[x]\) by finding a prime \(p\) such that \(f(x)\) is irreducible in \(\mathbb{Z}_p[x]\):
   - \(x^3 + 6x^2 + x + 6\)
   - \(7x^7 + x^6 + 9x^4 - 3x + 7\)

8. Provide an example of a polynomial \(f(x) \in \mathbb{Z}[x]\) and a prime \(p\) such that \(f(x)\) is reducible in \(\mathbb{Q}[x]\) but irreducible in \(\mathbb{Z}_p[x]\).

9. Give an example of a polynomial in \(\mathbb{Z}[x]\) that is irreducible in
Transcribed Image Text:Certainly! Below is the transcribed text formatted as if it were to appear on an educational website. --- ## Exercises on Polynomials and Irreducibility 1. Prove that the polynomial \(x^2 + x + 1\) has no roots in any field of characteristic 3. 2. Show details of the proof that if a monic polynomial with integer coefficients has a root in \(\mathbb{Q}\), then this root must be an integer. 3. If a monic polynomial with integer coefficients has a root in \(\mathbb{Q}\), show that this root must be an integer. 4. Demonstrate how each polynomial is irreducible in \(\mathbb{Q}[x]\), as seen in Example 3. - \(x^4 + 2x^2 + x + 1\) - \(x^4 + x^3 + x^2 + x + 1\) 5. Use Eisenstein's Criterion to show that each polynomial is irreducible in \(\mathbb{Q}[x]\): - \(x^4 - 4x + 22\) - \(5x^4 - 6x^3 + 36x - 6\) 6. Demonstrate that there are infinitely many integers \(k\) such that \(x^4 + 12x^2 - 21x + k\) is irreducible in \(\mathbb{Q}[x]\). 7. Show that each polynomial is irreducible in \(\mathbb{Z}[x]\) by finding a prime \(p\) such that \(f(x)\) is irreducible in \(\mathbb{Z}_p[x]\): - \(x^3 + 6x^2 + x + 6\) - \(7x^7 + x^6 + 9x^4 - 3x + 7\) 8. Provide an example of a polynomial \(f(x) \in \mathbb{Z}[x]\) and a prime \(p\) such that \(f(x)\) is reducible in \(\mathbb{Q}[x]\) but irreducible in \(\mathbb{Z}_p[x]\). 9. Give an example of a polynomial in \(\mathbb{Z}[x]\) that is irreducible in
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