Are Skew Lines Considered Perpendicular in 3D with Parallel Vectors?

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Discussion Overview

The discussion revolves around the concept of skew lines in three-dimensional space and whether they can be considered perpendicular based on the properties of their direction vectors. Participants explore the relationship between the dot product of vectors representing the lines and the conditions for intersection.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant proposes that if the dot product of the direction vectors of two skew lines is zero, then the lines should be considered perpendicular, but questions whether they must also intersect to be classified as such.
  • Another participant argues that while the lines can be considered orthogonal based on their direction vectors, this does not necessarily imply that they intersect, using the example of the x and y axes in different positions.
  • Further clarification is sought regarding the conditions under which perpendicular lines must intersect, particularly in the context of skew lines.
  • There is a reiteration that perpendicular lines only intersect if they lie in the same plane, suggesting that skew lines with perpendicular directions do not necessarily intersect.

Areas of Agreement / Disagreement

Participants generally agree that perpendicular lines do not have to intersect if they are skew, but there is ongoing discussion about the implications of orthogonality in relation to intersection.

Contextual Notes

The discussion highlights the nuances in defining perpendicularity and intersection in three-dimensional space, particularly concerning skew lines and their direction vectors.

mohamed el teir
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in 3D assume two skew lines L1: x=x°+at, y=y°+bt, z=z°+ct, L2: x=x°°+ds, y=y°°+es, z=z°°+fs. therefore L1, L2 parallel vectors are respectively: v1= <a, b, c>, v2= <d, e, f>. if v1.v2= ad+be+cf= 0 (vectors are perpendicular), are the line L1, L2 considered perpendicular also or beside the dot product of their parallel vectors being zero the lines must also intersect (must not be skew) ??
 
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The lines would be considered orthogonal, but that does not imply that they intersect.
Consider the x and y axes. The intersect in the plane z=0. But if you raise the x-axis to y=0, z=1, it will never intersect the y-axis defined by x=0, z=0.
 
RUber said:
The lines would be considered orthogonal, but that does not imply that they intersect.
Consider the x and y axes. The intersect in the plane z=0. But if you raise the x-axis to y=0, z=1, it will never intersect the y-axis defined by x=0, z=0.
do you mean that in the case that x-axis is in its original position the x and y axes are perpendicular and intersect, and in the case that the x-axis is in y = 0, z = 1 the x and y axes are perpendicular and doesn't intersect ?
 
mohamed el teir said:
do you mean that in the case that x-axis is in its original position the x and y axes are perpendicular and intersect, and in the case that the x-axis is in y = 0, z = 1 the x and y axes are perpendicular and doesn't intersect ?

Yes. Perpendicular lines only intersect if they lie in the same plane.
 
Yes. That was your question, right? If orthogonal lines must intersect or not.
 
RUber said:
Yes. That was your question, right? If orthogonal lines must intersect or not.
yes sort of that, if lines with perpendicular directions but the lines themselves are skew, are they considered perpendicular or not, so they are perpendicular, thank you
 

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