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GATE 2025 MA – Question 21

Real Analysis · Multivariable Analysis · 1 mark · Multiple choice

F:ℝ²→ℝ² is $F(x,y)=(x^3-3xy^2-3x,3x^2y-y^3-3y)$. Where is the inverse function theorem applicable?

  1. Everywhere
  2. Fails at exactly one point
  3. Fails at exactly two points
  4. Fails at exactly three points

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Correct answer: (C) Fails at exactly two points

Explanation

F represents the holomorphic polynomial z³−3z. Its real Jacobian determinant is $|3z^2-3|^2$, zero exactly at z=1 and z=−1. Everywhere else F is locally invertible. **C**.

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