- $ C = \\\left\\\{ {x \\\in \\\mathbb{Q}\\\left| {{x^2} + x - 12 = 0} \\\right.} \\\right\\\}.$
- $ A = \\\left\\\{ {x \\\in \\\mathbb{N}\\\left| {{x^2} - 4 = 0} \\\right.} \\\right\\\}.$
- $ B = \\\left\\\{ {x \\\in \\\mathbb{R}\\\left| {{x^2} + 2x + 3 = 0} \\\right.} \\\right\\\}.$
- $ B = \\\left\\\{ {x \\\in \\\mathbb{R}\\\left| {{x^2} - 5 = 0} \\\right.} \\\right\\\}.$