Finding Parametric Equations for Line: Perpendicular vs Parallel

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Discussion Overview

The discussion revolves around finding parametric equations for lines through a point that are either perpendicular or parallel to a given plane. Participants explore the differences in approach and reasoning for each case, including the implications of directionality and the mathematical representation involved.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that there is a fundamental difference in directionality when finding parametric equations for lines that are perpendicular versus parallel to a plane.
  • One participant notes that there is only one line through a point that is perpendicular to a surface, while there are infinitely many lines that can be parallel to the same surface.
  • Another participant suggests that the direction of the vector for the perpendicular line can be determined using the coefficients of the plane equation, which they later clarify as needing correction.
  • A participant provides the equation for a line perpendicular to a plane, indicating that it involves the normal vector of the plane, while also presenting a method for defining a line parallel to the plane using a vector in the plane.
  • There is acknowledgment that a line cannot be both parallel and perpendicular to the same plane simultaneously, indicating a need for clarity in the methods used to determine these lines.

Areas of Agreement / Disagreement

Participants generally agree on the distinction between perpendicular and parallel lines in relation to a plane, but there is some disagreement and confusion regarding the mathematical representation and the implications of the plane's equation.

Contextual Notes

Some participants express uncertainty about the correct formulation of the plane's equation and the implications of the coefficients used in determining the direction of the vector for the lines.

Who May Find This Useful

This discussion may be useful for students or individuals interested in understanding the geometric and algebraic principles involved in determining lines in three-dimensional space, particularly in relation to planes.

coleko
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Finding parametric equations for the line through the point that is perpendicular to plane and parallel?

What is the difference when finding parametric equations for a line through a point that is perpendicular vs. parallel? Surely there must be some difference but I cannot seem to figure it out.

Here is an example

Find parametric equations for the line through the point (2,4,6) perpendicular to plane x-y+3x=7
Also find parametric equations for the same line parallel to the same plane...

Do you find them both by using r(t)=r+ t*v
?
 
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coleko said:
Finding parametric equations for the line through the point that is perpendicular to plane and parallel?

What is the difference when finding parametric equations for a line through a point that is perpendicular vs. parallel? Surely there must be some difference but I cannot seem to figure it out.
They go in different directions.

Note, there is only one line through a point that is perpendicular to a surface, and an infinite number of possibilities parallel.

Here is an example

Find parametric equations for the line through the point (2,4,6) perpendicular to plane x-y+3x=7
Also find parametric equations for the same line parallel to the same plane...

Do you find them both by using r(t)=r+ t*v
?
Some issues with how you phrased that... what you have provided is not the equation of a plane (oh I suppose it could be - it would be 4x-y=7 for any z - so the plane does not intersect the z-axis) ... and "the same line" cannot be parallel. But yes you use the equation of a line both times - but that is not all you do. If r is the point then v must be a vector pointing in some direction: how do you determine that direction?
 
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To find the direction of the vector you would take the coefficients of the plane which would be <1,-1,3> I apologize because the 3x I wrote should really be 3z and the equation should read x-y+3z=7

I also realize that the same line cannot be parallel and perpendicular at the same time I am just questioning my methods on how to figure those out...
 


Well, a line through point P at position ##\vec{p}## perpendicular to a plane ##ax+by+cz+d=0## has equation: ##\vec{r}(t)=\vec{p}+\vec{n}t## where ##\vec{n}=(a,b,c)## is the normal to the plane.

A line parallel to the same plane would be and of ##\vec{r}(t)=\vec{p}+(a\vec{v}+b\vec{n}\times\vec{v})t## where ##\vec{v}## is any vector in the plane and ##a## and ##b## are arbitrary scalars.

See the difference?
 


Note that, in three dimensions, there exist a single line through a given point, perpendicular to a given plane but there exist and infinite number of lines through a given point parallel to the given plane.
 

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