The GATE Grind

GATE 2022 MA – Question 37

Algebra · Rings and Ideals · 2 marks · Multiple choice

For proper nonzero ideals J₁,J₂ of a nonzero commutative ring R, P:for every r₁,r₂∈R there is a unique r∈R with r−r₁∈J₁,r−r₂∈J₂. Q:J₁+J₂=R. Which implication holds?

  1. P⇒Q but not conversely
  2. Q⇒P but not conversely
  3. Both implications
  4. Neither implication

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) P⇒Q but not conversely

Explanation

P gives existence for r₁=0 and arbitrary r₂, writing r₂ as a sum of an element of J₁ and one of J₂, hence Q. Comaximality guarantees existence only modulo J₁∩J₂, not uniqueness as an actual ring element. In ℤ, J₁=2ℤ,J₂=3ℤ are comaximal but any solution can be shifted by 6. Thus **A**.

More Rings and Ideals questions

All Rings and Ideals questions →