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GATE 2021 ST – Question 42

Joint Distributions · Functions of Random Vectors · 2 marks · Multiple choice

X∼Uniform[−π/2,π/2]. Which statement is NOT true?

  1. cot X is standard Cauchy.
  2. tan X is standard Cauchy.
  3. −ln(1/2+X/π) has MGF 1/(1−t),t<1.
  4. −2ln(1/2+X/π) is central χ² with one degree of freedom.

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Correct answer: (D) −2ln(1/2+X/π) is central χ² with one degree of freedom.

Explanation

Tan of a uniform angle is standard Cauchy;its reciprocal cot has the same law. The transformed U=1/2+X/π is Uniform(0,1),so −ln U∼Exp(1). Consequently −2ln U is χ²₂,not χ²₁. **D**.

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