Line of intersection between two parallel planes?

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Discussion Overview

The discussion revolves around finding the line of intersection between two parallel planes represented by the equations 2x - y + 2z + 1 = 0 and -4x + 2y - 4z - 2 = 0. Participants explore the implications of the planes being parallel, including the nature of their intersection and how to express this intersection in parametric, Cartesian, and vector forms.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant identifies that the two planes are parallel and expresses uncertainty about how to find the intersection point.
  • Another participant clarifies that parallel planes either coincide (same plane) or do not intersect at all, leading to a discussion about the nature of their intersection.
  • Some participants argue that since the planes are the same, they intersect at infinitely many points, suggesting that any two points within the plane can define a line.
  • There is a suggestion to find specific points on the plane to describe the line through them, with one participant providing calculations for points based on the plane equation.
  • Participants discuss the need to express the intersection in different forms despite the infinite nature of the intersection.
  • There is a correction regarding a typographical error in the equations, where one participant points out that "4x" should be "4z".

Areas of Agreement / Disagreement

Participants generally agree that the two planes are the same and thus intersect at infinitely many points. However, there is no consensus on how to express this intersection in the requested forms, leading to ongoing questions and exploration of possible solutions.

Contextual Notes

Participants express uncertainty about how to represent the infinite intersection in parametric, Cartesian, and vector forms, indicating a need for further clarification on how to approach this task.

sawdee
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How can I find the line of intersection between the planes 2x-y+2x+1=0 and -4x+2y-4x-2=0

I realize these are parallel as they are multiples of each other, but I'm not sure how to solve for the point. I also have to convert this line into parametric, cartesian and vector form.

Sorry for the continuous posts, I have an exam tomorrow and I'm stuck on these questions :/ Can't ask a teacher either.
 
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When two planes are parallel, you have 2 options:

i) they are the same plane...they then intersect over the entire plane defined by both.

ii) they are distinct...and so they intersect nowhere.
 
MarkFL said:
When two planes are parallel, you have 2 options:

i) they are the same plane...they then intersect over the entire plane defined by both.

ii) they are distinct...and so they intersect nowhere.

In terms of that, how can I solve for the question? Is there a way to find this parallel point of intersection?
 
sawdee said:
In terms of that, how can I solve for the question? Is there a way to find this parallel point of intersection?

The two planes you gave are the same plane, so they "intersect" at infinitely many points...consisting of the entire plane the two equations define.
 
MarkFL said:
The two planes you gave are the same plane, so they "intersect" at infinitely many points...consisting of the entire plane the two equations define.

Hmm that does make sense, however the question still asks for the three forms of the line of intersection (parametric, vector and Cartesian). Do i simply write there are infinite solutions, or is there a way to find one?
 
sawdee said:
Hmm that does make sense, however the question still asks for the three forms of the line of intersection (parametric, vector and Cartesian). Do i simply write there are infinite solutions, or is there a way to find one?

Since the two planes are the same, there are an infinite number of lines within the intersection...there is no one line that is a "best choice." If you are forced to define one line within the given plane, then you could pick any two points within the given plane and construct the line passing through these two points.

Also, you are typing "x" when I think you mean "z"...so let's look at this definition of the given plane:

$$2x-y+2z+1=0$$

If we let $(y,z)=(0,0)$ we find:

$$x=-\frac{1}{2}$$

And if we let $(x,z)=(0,0)$ we find:

$$y=1$$

And so we have the two points:

$$\left(-\frac{1}{2},0,0\right),\,\left(0,1,0\right)$$

Can you take these two points and describe the line through them?
 
MarkFL said:
Since the two planes are the same, there are an infinite number of lines within the intersection...there is no one line that is a "best choice." If you are forced to define one line within the given plane, then you could pick any two points within the given plane and construct the line passing through these two points.

Also, you are typing "x" when I think you mean "z"...so let's look at this definition of the given plane:

$$2x-y+2z+1=0$$

If we let $(y,z)=(0,0)$ we find:

$$x=-\frac{1}{2}$$

And if we let $(x,z)=(0,0)$ we find:

$$y=1$$

And so we have the two points:

$$\left(-\frac{1}{2},0,0\right),\,\left(0,1,0\right)$$

Can you take these two points and describe the line through them?

Yes sorry, that 4x is supposed to be 4z!

So you mean solve for each component (x,y,z) of the first plane equation and use those 3 points as in the intercepting points?
 
sawdee said:
Yes sorry, that 4x is supposed to be 4z!

So you mean solve for each component (x,y,z) of the first plane equation and use those 3 points as in the intercepting points?

No, I mean can you find the line passing through the two points I gave?
 

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