Deodorant Cap (AR Modeling Challenge)

This [b][color=#0000ff]deodorant cap[/color][/b] looks like a hyperbolic paraboloid. [br][br]The equation of the [b][color=#1e84cc]blue surface[/color][/b] used to graph this within GeoGebra Augmented Reality can be seen at the bottom of the screen. Note the restrictions placed on the domain of this surface function. [br][br][b]Questions:[/b][br][br]1) What is the equation of the [b][color=#ff00ff]pink plane[/color][/b] (at the bottom)? [br][br]2) What are the domain restrictions of this surface equation? [br][br]After answering questions (1) and (2), check the accuracy of your responses by graphing both surfaces in GeoGebra Augmented Reality! [br][br]Other than a [url=https://www.geogebra.org/m/yuqhawzv]Pringles potato chip[/url], what other every-day, real-life, 3D objects look like hyperbolic paraboloids?
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Information: Deodorant Cap (AR Modeling Challenge)