The GATE Grind

GATE 2026 MA – Question 49

Topology · Connectedness and Compactness · 2 marks · Multiple select

$S=\bigcup_{n=1}^\infty\{(x,y)\in\mathbb R^2:(x-n)^2+y^2=1/n^2\}$ with the usual topology. Which statements hold?

  1. S is not compact.
  2. S is compact.
  3. S is connected.
  4. S is not connected.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) S is not compact.; (D) S is not connected.

Explanation

Points (n+1/n,0) belong to S and escape to infinity, so S is unbounded and not compact. Circles n=1,2 have x≤2.5; every circle n≥3 has x≥3−1/3=8/3. The vertical line x=2.6 therefore separates two nonempty relatively open subsets of S. Hence it is disconnected. **A,D**.

More Connectedness and Compactness questions

All Connectedness and Compactness questions →