Visualizing a strange quadric surface

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Discussion Overview

The discussion revolves around visualizing the quadric surface defined by the equation x^2 + y^2 + z^2 = z. Participants explore methods to simplify and understand the geometric representation of this surface.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant requests assistance in visualizing the quadric surface given by the equation x^2 + y^2 + z^2 = z.
  • Another participant suggests performing algebraic manipulations such as completing the square to simplify the equation.
  • A participant introduces the general form of a sphere, (x-a)^2 + (y-b)^2 + (z-c)^2 = d, to provide context for understanding the surface.
  • Further simplification leads to the equation x^2 + y^2 + (z - 1/2)^2 = 1/4, indicating a sphere centered at (0, 0, 1/2) with a radius of 1/2.
  • There is a confirmation that the derived surface is indeed a sphere centered at (0, 0, 1/2) with the stated radius.

Areas of Agreement / Disagreement

Participants generally agree on the interpretation of the surface as a sphere, with some confirming the calculations and conclusions drawn from the algebraic manipulations.

Contextual Notes

The discussion involves algebraic transformations that depend on the accuracy of the mathematical steps taken, particularly in completing the square and interpreting the resulting equation.

Woland
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Hi all,

I am trying to visualize the following quadric surface:
x^2 + y^2 + z^2 = z

Could someone please help me understand what this surface looks like? I could not find an example of this one on the internet.

Thank you.
 
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Do some algebra to simplify it. (e.g. things like collecting similar terms, completing the square, factoring, change of variable, etc)
 
Consider what the surface
(x-a)^2 + (y-b)^2 + (z-c)^2 = d

looks like
 
(x-a)^2 + (y-b)^2 + (z-c)^2 = d is a sphere centered at a, b, c with radius square root of d.

Now regarding the first post, I can bring the z over to the left hand side:

x^2 + y^2 + z^2 - z = 0

Then complete the square

x^2 + y^2 + (z - 1/2)^2 -1/4 = 0
[(z - 1/2)^2 = z^2 - 2*1/2 z + 1/4]

Then

x^2 + y^2 + (z-1/2)^2 = 1/4

This means that this is a sphere centered at 0,0, 1/2. Is that correct?
 
This means that this is a sphere centered at 0,0, 1/2. Is that correct?

Yes and the radius is 1/2.
 

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