Tập nào sau đây là không gian con của R3:

\[{\rm{W}} = \left\{ {({{\rm{x}}_{\rm{1}}}{\rm{,}}{{\rm{x}}_{\rm{2}}}{\rm{,}}{{\rm{x}}_{\rm{3}}}{\rm{/}}{{\rm{x}}_{\rm{1}}} = 0} \right\} \subset {{\rm{R}}^3}\]

\[{\rm{W}} = \left\{ {({{\rm{x}}_{\rm{1}}}{\rm{,}}{{\rm{x}}_{\rm{2}}}{\rm{,}}{{\rm{x}}_{\rm{3}}}{\rm{/}}{{\rm{x}}_{\rm{1}}} = 1} \right\} \subset {{\rm{R}}^3}\]

\[{\rm{W}} = \left\{ {({{\rm{x}}_{\rm{1}}}{\rm{,}}{{\rm{x}}_{\rm{2}}}{\rm{,}}{{\rm{x}}_{\rm{3}}}{\rm{/}}{{\rm{x}}_{\rm{1}}}{\rm{ + }}{{\rm{x}}_{\rm{2}}} = 1} \right\} \subset {{\rm{R}}^3}\]

\[{\rm{W}} = \left\{ {({{\rm{x}}_{\rm{1}}}{\rm{,}}{{\rm{x}}_{\rm{2}}}{\rm{,}}{{\rm{x}}_{\rm{3}}}{\rm{/}}{{\rm{x}}_{\rm{2}}} = 3} \right\} \subset {{\rm{R}}^{\rm{3}}}\]