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GATE 2021 MA – Question 20

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

Let f:(−π/2,π/2)→ℝ be f(x)=π/2+x−arctan x. P:|f(x)−f(y)|<|x−y| for all x,y in the domain. Q:f has a fixed point. Choose truth values.

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

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Show answer and explanation

Correct answer: (D) Both false

Explanation

As printed, P includes x=y, which would require 0<0, so P is false. For distinct x,y, f′(x)=x²/(1+x²)<1 and the mean-value theorem would give the strict inequality. Q requires arctan x=π/2, impossible at any finite x. Under the literal stated quantifier both are false, **D**. The distinction about equal arguments is essential.

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