Show that the subsets of the plane are open:(adsbygoogle = window.adsbygoogle || []).push({});

1.) A= {(x,y)|-1<x<1,-1<y<1}

2.) C= {(x,y)|2<x^{2}+ y^{2}<4}

I have no clue on how to start with this problem.

I have another question. What does this notation imply. f(x,y)=some function.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Show subsets of the plane are open

**Physics Forums | Science Articles, Homework Help, Discussion**