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Consider the set :

\[ A = \{(x, y) \,/\, xy = 0\} \]

Which of the following is false ?

  • A.A is closed in \(\mathbf{R}^{2}\)
  • B.A is path connected
  • C.A is connected
  • D.A is not connected

Answer: D

The false statement is A is not connected.

The set \(xy = 0\) is the union of the two coordinate axes. It is the zero set of the continuous function \(xy\), so it is closed in \(\mathbf{R}^{2}\).

Any point on the x-axis can be joined to the origin along that axis, and the origin to any point on the y-axis along the other, so A is path connected and hence connected. That makes 'A is not connected' the false statement.

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