Parallel Planes: Same/Opposite Sides of Origin?

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Discussion Overview

The discussion revolves around the interpretation of the equation of a plane, specifically regarding the conditions under which two planes are considered to be on the same or opposite sides of the origin. The scope includes theoretical considerations of plane equations and their geometric implications, particularly focusing on parallel planes.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant cites a book stating that two planes with the same sign for ##d## are on the same side of the origin, while those with different signs are on opposite sides, questioning if this applies strictly to parallel planes.
  • Another participant emphasizes the need to clarify what "same side of the origin" means for non-parallel planes.
  • A subsequent post reiterates the need for clarity regarding parallel planes, suggesting that multiplying both sides of the plane equation by -1 does not alter the position of the plane.
  • Another participant agrees, stating that for the parallel plane scenario to hold, the coefficients a, b, and c must remain constant or proportional without changing signs.

Areas of Agreement / Disagreement

Participants express uncertainty about the application of the same/opposite side concept to non-parallel planes, indicating that multiple views remain regarding the interpretation of the conditions for parallel planes.

Contextual Notes

The discussion does not resolve the definitions or implications of "same side of the origin" for non-parallel planes, nor does it clarify the conditions under which the properties of parallel planes hold.

PFuser1232
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According to my book, if we write the equation of a plane as:

##ax + by + cz = d##

And two planes have values of ##d## with the same sign, they are on the same side of the origin. If they have values of ##d## with different signs, they are on opposite sides of the origin.

I'm confused as to whether this applies strictly to two parallel planes, or any pair of planes.
 
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You must decide what "same side of the origin" means for non-parallel planes.
 
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jbriggs444 said:
You must decide what "same side of the origin" means for non-parallel planes.

What about parallel planes? If both sides of the plane equation (cartesian form) are multiplied by -1, the position of the plane is unaltered, right?
 
Right. In order to make the "parallel plane" version work, you need for a, b and c to either remain constant or at least to remain proportional and not change signs.
 

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