Sorry if this is a stupid question to ask. This is an exercise from Gathmann's Algebraic Geometry.
Show that every affine variety in the real affine space $A^n_R$ is the zero locus of one polynomial.
If some context might help, he is talking about dimension of a topological spaces in that section. In the same problem, he asks to show that every Noetherian topological space is compact, which is easier to show.
I have no idea where to start. Please give me some hint. Thank you so much!