Find a point in a line closest to another point

In summary, to find the coordinates of the point on a line closest to a given point, we first find the equation of the line and then use the condition that the vector from the closest point to the given point must be perpendicular to the line. This results in a system of equations, which can be solved to find the coordinates of the closest point. In this case, the closest point on line L to point R is (2, 0, 7).
  • #1
fireb
11
0

Homework Statement


Given p(4,2,3), Q(5,3,1), R(3,-5,5) and let L be a line that passes through P and Q
Find the coordinates of that point of the line L which is closest to the point R.


Homework Equations





The Attempt at a Solution


I found the equation of the line L= (x=4+t, y=2+t, z=3-2t) then i am unsure on how to find the coordinates closest to R.
Any hints on solving this will be appreciated.
Thanks in Advance
 
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  • #2
the vector from the closest point of the line to the point will be perpindicular to the line (why?)
 
  • #3
lanedance said:
the vector from the closest point of the line to the point will be perpindicular to the line (why?)
(
I think i got it now...

So if we let A(x,y,z) be the closest point from L to R. This condition must be satisfy: RA dot PQ= 0. SO RA = (3-x,-5-y,5-z).
And from the dot product, i get x+y-2z=-12. So, i sub in the L into the equation I just got and solve for t, and equal t=-2, yields x=2
y=0,z=7. So A is (2,0,7)?
Can someone correct me if i am wrong

Thanks
 
Last edited:
  • #4
if vectors a & b are perpindicular then:
a x b is a non-zero vector
a . b is zero...
 

1. How do you find the closest point on a line to another point?

To find the closest point on a line to another point, you can use the formula for the shortest distance between a point and a line. This involves finding the perpendicular distance from the given point to the line, and then finding the point on the line that is closest to the given point.

2. What is the formula for finding the shortest distance between a point and a line?

The formula for finding the shortest distance between a point and a line is d = |ax0 + by0 + c| / √(a^2 + b^2), where (x0, y0) is the coordinates of the given point, and a, b, and c are the coefficients of the line's equation in standard form (ax + by + c = 0).

3. Can you use this formula to find the closest point on a line to a point that is not on the line?

Yes, the formula for finding the shortest distance between a point and a line can be used to find the closest point on a line to a point that is not on the line. It will give you the coordinates of the point on the line that is closest to the given point.

4. What if the line is not a straight line but a curve?

The formula for finding the shortest distance between a point and a line applies to straight lines only. For curved lines, you can find the closest point by finding the tangent to the curve at the given point and then finding the intersection point of the tangent and the line.

5. Is there a quicker way to find the closest point on a line to another point?

Yes, there are other methods for finding the closest point on a line to another point, such as using vectors or linear algebra. These methods may be quicker and more efficient for certain types of problems, but the formula for finding the shortest distance between a point and a line is a commonly used approach that works for all types of lines.

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