Do lines have to be intersecting in order to be perpendicular?

  • Context: High School 
  • Thread starter Thread starter The Rev
  • Start date Start date
  • Tags Tags
    Geometry
Click For Summary

Discussion Overview

The discussion revolves around the definition of perpendicularity in the context of lines and planes, particularly in three-dimensional Euclidean geometry. Participants explore whether lines must intersect to be considered perpendicular and how this concept applies to vectors and lines in a plane.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions if lines need to intersect to be perpendicular, specifically asking about lines perpendicular to a plane and their relationship with lines on that plane.
  • Another participant asserts that in three-dimensional Euclidean geometry, a line perpendicular to a plane is considered perpendicular to all lines in that plane, regardless of intersection.
  • A different participant notes that there is no standard definition of perpendicular lines in three-dimensional space, indicating that some definitions may require intersection while others do not.
  • One participant suggests that the term "perpendicular" is more commonly applied to vectors, proposing that two lines could be defined as perpendicular if their direction vectors are perpendicular, with intersection being a possible requirement depending on the context.

Areas of Agreement / Disagreement

Participants express differing views on whether perpendicular lines must intersect, indicating that multiple competing definitions and interpretations exist within the discussion.

Contextual Notes

There is a lack of consensus on the definition of perpendicularity in three-dimensional space, with participants highlighting the dependence on context and definitions used in different sources.

The Rev
Messages
81
Reaction score
0
Do lines have to be intersecting in order to be perpendicular?

For example, is a line which is perpendicular to a plane perpendicular to only the lines on that plane which intersect with it, or ALL lines on that plane?

Thanks.

[tex]\pi[/tex]

The Rev
 
Mathematics news on Phys.org
No,of course not,once u consider euclidean geometry in 3 dimensions.I think u gave the answer yourself.A line perpendicular to a plane is perpendicular on any line from that plane.And obviously the 2 lines are not coplanar & don't intersect...

Daniel.
 
Like being parallel, there isn't really a standard way of defining perpendicular lines in 3-space. Some prefer them to be intersecting, others not.
 
Maybe it's just me but I always thought of perpendicular as being a term that applies to vectors not lines. So a plane is perpendicular to a vector x if all the vectors in the plane (not lines) were perpendicular the the vector x. Since vectors intersect at the origin there's no real confusion.

I guess it should be easy to extend this definition of lines just by saying two lines are perpendicular if their direction vectors are perpendicular. Or you could require intersection. I guess it depends on the source you are working with.
 

Similar threads

  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 2 ·
Replies
2
Views
6K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 12 ·
Replies
12
Views
3K
Replies
24
Views
2K