Prove that the distance between point-line is given by some formula

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Homework Help Overview

The discussion revolves around proving a formula for the distance between a point and a line in vector terms. The original poster presents a specific vector-based expression involving the cross product of two vectors, one from the point to the line and another parallel to the line.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants suggest starting by identifying the vectors involved, questioning whether a formal proof is necessary or if a diagram would suffice. There is discussion about the geometric interpretation of the vectors and their norms, particularly in relation to the area of a parallelogram.

Discussion Status

The conversation is ongoing, with participants exploring different interpretations of the vectors and their geometric meanings. Some guidance has been offered regarding the relationship between the vectors and the area they define, but no consensus has been reached on how to proceed with the proof.

Contextual Notes

There is an emphasis on the need for an algebraic proof, and participants are grappling with the definitions and relationships of the vectors involved, particularly regarding the interpretation of the norm of vector v.

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Homework Statement



Show that if u is a vector from any point on a line to a point P not on the line, and v is a vector parallel to the line, then the distance between P and the line is given by

NORM of u x v / NORM v

u x v--> cross product of u and v


I know how to calculate the distance between a point and a line, but I just don't know how to start proving this...

any help please?

thanks a lot
 
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Well, you could start by working out what the vectors u and v are.
 
Do you need to formally prove this or is a picture showing it's true enough? It's pretty easy to show why it's true using a diagram.
 
Use u x v = |u| |v| cos(theta)
 
uart said:
Use u x v = |u| |v| cos(theta)
You mean sin θ, right?
 
vela said:
You mean sin θ, right?


yeah, its sinθ ... but I still don't quite get how to do it...

And also, yes, I believe you have to prove it algebraically or something
 
Ok, so we know that the norm of uxv is the area of the parallelogram formed by u and v...
The norm of v has no geometric interpretation (its just the length of a line)

How can we relate this so it gives the distance between P and the line...

any more ideas??
 
aero_zeppelin said:
Ok, so we know that the norm of uxv is the area of the parallelogram formed by u and v...
The norm of v has no geometric interpretation (its just the length of a line)
No and no. The norm of a vector v has a perfectly good geometric interpretation - it's the length of the vector. A line has infinite length - maybe you meant line segment?
aero_zeppelin said:
How can we relate this so it gives the distance between P and the line...

any more ideas??
 
Mark44 said:
No and no. The norm of a vector v has a perfectly good geometric interpretation - it's the length of the vector. A line has infinite length - maybe you meant line segment?

yeah, line segment. Anyway... I just don't know how to relate both of these.

Is the norm of v considered the "base" of the parallelogram?
 

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