- $ \\\left\\\{ {{\\\text{x}} \\\in \\\mathbb{R}\\\left| {{x^2} - 4x + 3 = 0} \\\right.} \\\right\\\}$.
- $ \\\left\\\{ {{\\\text{x}} \\\in \\\mathbb{Q}\\\left| {{{\\\text{x}}^{\\\text{2}}} - 4x + 2 = 0} \\\right.} \\\right\\\}$.
- $ \\\left\\\{ {{\\\text{x}} \\\in \\\mathbb{Z}\\\left| {6{x^2} - 7x + 1 = 0} \\\right.} \\\right\\\}$.
- $ \\\left\\\{ {{\\\text{x}} \\\in \\\mathbb{Z}\\\left| {\\\left| {\\\text{x}} \\\right| < 1} \\\right.} \\\right\\\}$.