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

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In summary, the distance between a point P and a line can be calculated by using the norm of the cross product of a vector u from any point on the line to P and a vector v parallel to the line, divided by the norm of v. This can be proven by using the formula for the cross product and understanding that the norm of v represents the base of the parallelogram formed by u and v, which can then be used to find the distance between P and the line.
  • #1
aero_zeppelin
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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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  • #2
Well, you could start by working out what the vectors u and v are.
 
  • #3
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.
 
  • #4
Use u x v = |u| |v| cos(theta)
 
  • #5
uart said:
Use u x v = |u| |v| cos(theta)
You mean sin θ, right?
 
  • #6
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
 
  • #7
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??
 
  • #8
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??
 
  • #9
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?
 

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

What is the distance between a point and a line?

The distance between a point and a line is the shortest distance between the point and any point on the line. It is the length of the perpendicular line segment drawn from the point to the line.

What is the formula for calculating the distance between a point and a line?

The formula for calculating the distance between a point and a line is:
d = |Ax + By + C| / √(A² + B²)
where A, B, and C are the coefficients of the line's equation, and (x, y) are the coordinates of the point.

How do I determine the coefficients of a line's equation?

The coefficients of a line's equation can be determined using the slope-intercept form:
y = mx + b
where m is the slope of the line and b is the y-intercept. The coefficients can also be determined using the point-slope form:
y - y1 = m(x - x1)
where (x1, y1) is a point on the line and m is the slope of the line.

Can the distance between a point and a line be negative?

No, the distance between a point and a line cannot be negative. It is always a positive value, as it represents the length of a line segment.

Is there a visual representation of the distance between a point and a line?

Yes, the distance between a point and a line can be visualized as a right triangle, with the point being one of the vertices and the line being the hypotenuse. The distance is equal to the length of the altitude drawn from the point to the line.

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