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The equation \(\mathrm{Im}(1 - i)z = 1\) represents the line

  • A.\(y = x + 1\)
  • B.\(y = 1 - x\)
  • C.\(y = x - 1\)
  • D.\(y = x + 2\)
  • E.\(y = -x - 1\)

Answer: A

The equation represents the line \(y = x + 1\).

Write \(z = x + iy\) and multiply out.

\[ \begin{aligned} (1 - i)(x + iy) &= x + iy - ix - i^{2}y \\ &= (x + y) + i(y - x) \end{aligned} \]

The imaginary part is \(y - x\), so \(y - x = 1\), that is \(y = x + 1\). Taking the real part by mistake gives \(x + y = 1\), the option \(y = 1 - x\), and a sign slip in \(-i^{2}y\) produces the other lines.

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