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Part CCSIR NET December 2025eisenstein-only-blesses-the-cubic-the-other-two-quadratics-factor-by-inspection

Eisenstein only blesses the cubic the other two quadratics factor by inspection

Which of the following statements are true?

  1. A.x2+x^{2} + xy2xy+1^{2} - x - y + 1 is irreducible in Q[x,y]\mathbb{Q}[x,y].
  2. B.x3+100x2+25x+10x^{3} + 100x^{2} + 25x + 10 is irreducible in Z[x]\mathbb{Z}[x].
  3. C.2x2+32x^{2} + 3xy +y2+3x+2y+1+ y^{2} + 3x + 2y + 1 is irreducible in Q[x,y]\mathbb{Q}[x,y].
  4. D.x4+4x2+3x^{4} + 4x^{2} + 3 is irreducible in Z[x]\mathbb{Z}[x].

You have the answer. Trap Analysis is why the other three were written.

Not a worked solution repeated four times — the specific reasoning error each wrong option was built to reward.

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50 are analysed free — try those first.

Related counterexample: Irreducible over ℤ ⇒ irreducible mod every prime

More on this topic

The chapter behind this: Irreducibility tests — free to read

From Rings and FieldsPolynomial rings and irreducibility tests

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