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GATE 2023 MA – Question 20

Real Analysis · Metric Spaces and Continuity · 1 mark · Multiple choice

In C[0,1] with supremum metric let X={f:‖f‖∞≥1/2}. Set f₁(x)=x and f₂(x)=1−x. P:f₁ lies in int X. Q:f₂ lies in int X. Choose truth values.

  1. P true, Q false
  2. P false, Q true
  3. Both false
  4. Both true

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Show answer and explanation

Correct answer: (D) Both true

Explanation

Both functions have norm 1. If ‖g−f_i‖∞<1/2, the reverse triangle inequality gives ‖g‖∞>1/2. Thus each has an open ball contained in X and both are interior points. **D**.

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