The GATE Grind

GATE 2022 MA – Question 36

Algebra · Rings and Ideals · 2 marks · Multiple choice

Which describes ℝ[X]/(X⁴+4)?

  1. A field
  2. An integral domain but not a field
  3. Not an integral domain, but zero is its only nilpotent
  4. Contains nonzero nilpotents

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Correct answer: (C) Not an integral domain, but zero is its only nilpotent

Explanation

Factor X⁴+4=(X²−2X+2)(X²+2X+2). Both factors are distinct irreducible real quadratics. The Chinese remainder theorem gives a product of two fields, ℂ×ℂ. It has zero divisors, but an element is nilpotent only when both field components are zero. **C**.

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