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 February 14th, 2010, 09:53 AM #1 Member   Joined: Sep 2007 Posts: 49 Thanks: 0 Surface Describe th surface: x^2-y^2=1 So if it's in 2-D, it's must be hyperbolas. However, if I put it in 3-D, I'm unsure because according to what's written on my book, it says If one of the variables x,y or z is missing from the equation of a surface, then the surface is a cylinder. Though I was considering other options like Hyperbolic Paraboloid, but the only problem is the general formula is z/c=x^2/a^2 - y^2/b^2, and there is a z here. In that case, usually we can set z to 0, and so on. But in my original equation, z is never there, so that's the part I'm confused about. Thanks for help.
 February 14th, 2010, 12:32 PM #2 Global Moderator   Joined: Dec 2006 Posts: 20,104 Thanks: 1907 Believe the book.
 February 14th, 2010, 02:09 PM #3 Senior Member   Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3 Re: Surface It's a cylinder -- but not the ordinary kind. It's a hyperbolic cylinder. If you imagine the xy plane as the page of a book, and the z axis as pointing out of the page, then you can envision drawing the graph of x²-y² = 1 on the page, and then building a cardboard wall upwards from the graph.
 February 15th, 2010, 07:54 PM #4 Member   Joined: Sep 2007 Posts: 49 Thanks: 0 Re: Surface Thanks, aswoods. It helps a lot!!

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