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GATE 2010 CS (CS1) – Question 14

Engineering Mathematics · Discrete Mathematics: Monoids and Groups · 1 mark · Multiple choice

S={1,ω,ω²}, where ω and ω² are cube roots of unity. Under multiplication, (S,*) forms

  1. a group
  2. a ring
  3. an integral domain
  4. a field

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Show answer and explanation

Correct answer: (A) a group

Explanation

Multiplication is associative, closed because ω³=1, and has identity one. Inverses are 1⁻¹=1, ω⁻¹=ω² and (ω²)⁻¹=ω. Thus S is the cyclic multiplicative group of order three, A. The other structures require an additional addition operation.

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