- #1
mateomy
- 307
- 0
[tex]
Let\,S=\,\{(x,y)\,\in\,\mathbb{R}^2\,|\,xy\,>\,1\}
[/tex]
Show S is open.
I've been reading everything I can get my hands on to get a handle on these sort of proofs. I think I have the definitions of everything down solid but my problem seems to be proving things for myself as I think is true for almost everyone who is first confronted with this stuff. This is what I've done so far...
Let xy be defined as a point q. We define a point z [itex]\in[/itex] D(w,r), where [itex]r=\frac{1}{2}d(w,q)[/itex].
Further;
d(w,q) [itex]\leq[/itex] d(q,z) + d(z,w).
Hence, d(q,z) [itex]\geq[/itex] d(w,q) - d(z,w)
I don't know where to move from here. I'm not even sure if I'm on the right track. I know I can substitute d(w,q) as 2r but I don't know if that will help me at all. Also (for clarification) 'D(w,r)' is my 'ball' in [itex]\mathbb{R}^2[/itex] centered at 'w' with a radius 'r'.
Thanks for the help.
Let\,S=\,\{(x,y)\,\in\,\mathbb{R}^2\,|\,xy\,>\,1\}
[/tex]
Show S is open.
I've been reading everything I can get my hands on to get a handle on these sort of proofs. I think I have the definitions of everything down solid but my problem seems to be proving things for myself as I think is true for almost everyone who is first confronted with this stuff. This is what I've done so far...
Let xy be defined as a point q. We define a point z [itex]\in[/itex] D(w,r), where [itex]r=\frac{1}{2}d(w,q)[/itex].
Further;
d(w,q) [itex]\leq[/itex] d(q,z) + d(z,w).
Hence, d(q,z) [itex]\geq[/itex] d(w,q) - d(z,w)
I don't know where to move from here. I'm not even sure if I'm on the right track. I know I can substitute d(w,q) as 2r but I don't know if that will help me at all. Also (for clarification) 'D(w,r)' is my 'ball' in [itex]\mathbb{R}^2[/itex] centered at 'w' with a radius 'r'.
Thanks for the help.