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The set \(\{z \in \mathbf{C} : |e^{z}| = 2019\}\) represents :

  • A.the line \(x = \log(2019)\)
  • B.the line \(y = 2019\)
  • C.a circle
  • D.a countable set

Answer: A

The set is the line \(x = \log(2019)\).

For \(z = x + iy\), \(e^{z} = e^{x}e^{iy}\) and \(|e^{iy}| = 1\), so \(|e^{z}| = e^{x}\). The condition \(e^{x} = 2019\) gives \(x = \log 2019\) with \(y\) arbitrary: a vertical line in the plane.

The modulus does not depend on \(y\) at all, so \(y = 2019\) is wrong, and the set is neither a circle nor countable (it contains a point for every real \(y\)). A circle would come from \(|z| = \text{const}\), not \(|e^{z}| = \text{const}\).

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