Equation of a line perpendicular to 2 vectors

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Homework Help Overview

The problem involves finding the equation of a line in R3 that passes through the point (-1,1,2) and is perpendicular to two given vectors, V1 (-1,1,-1) and V2 (1,1,1). The original poster attempts to derive the line's equation in parametric form but expresses uncertainty about the correctness of their approach.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the original poster's attempt to use vector V2 for the line's direction and question its validity regarding perpendicularity. There is also a mention of finding equations for lines perpendicular to each vector individually, but uncertainty remains about how to find a direction vector that is perpendicular to both V1 and V2.

Discussion Status

The discussion is ongoing, with participants exploring different approaches to find a suitable direction vector. Some guidance has been offered regarding the need for a vector that is perpendicular to both V1 and V2, and a question about the cross product of the two vectors has been raised.

Contextual Notes

There is a lack of clarity regarding the method to find a vector that is perpendicular to both V1 and V2, and the original poster expresses confusion about the correctness of their initial solution.

Bertrandkis
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Homework Statement



Let L be a line in R3 passing through(-1,1,2) and is perpendicular to vectors V1 (-1,1,-1)
and V2 (1,1,1). Find an equation for L in parametric form.

Homework Equations





The Attempt at a Solution


using vector V2
(x,y,z)(1,1,1)=(1,1,1)(-1,1,2)
A possible equation for L=>(x,y,z)=(-1,1,2)+t(1,1,1)

I don't know if I am right.
 
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Bertrandkis said:

Homework Statement



Let L be a line in R3 passing through(-1,1,2) and is perpendicular to vectors V1 (-1,1,-1)
and V2 (1,1,1). Find an equation for L in parametric form.

Homework Equations





The Attempt at a Solution


using vector V2
(x,y,z)(1,1,1)=(1,1,1)(-1,1,2)
A possible equation for L=>(x,y,z)=(-1,1,2)+t(1,1,1)

I don't know if I am right.
The line you give is not perpendicular to V2. Any point on (-1,1,2)+ t(1,1,1) has position vector (t-1, t+1, t+ 2) and its dot product with (1, 1, 1) is (t-1)+ (t+1)+ (t+2)= 3t+2, not 0. I'm not sure why you think that would give you a line perpendicular to (1,1,1).

But even if you were to find a line perpendicular to V2, there is no reason to think that line would also be perpendicular to V1! You need a direction vector that is perpendicular to both. Do you know how to calculate a vector perpendicular to both V1 and V2?
 
To be honest, I don't know how to find a vector perpendicular to both V1 and V2.
I can find 2 equations of a lines perpendicular to each of the vectors
(1)=> (x,y,z)=(-1,1,2)+t(-1,1,1)
(2)=> (x,y,z)=(-1,1,2)+t(1,1,1)
now where do I go from here.
 
Do you know what the cross product of two vectors is?
 

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