Finding a Perpendicular Vector in 3D Space

  • Thread starter SigmaCrisis
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In summary, in order to find a vector that is perpendicular to the plane formed by three points in 3D space (P, Q, and R), you can first draw two vectors from any of the points to other points. These two vectors are parallel to the plane. Then, using the cross product, you can find a vector that is perpendicular to the plane. To find the area of the triangle PQR, you can use the magnitude of the cross product, which is also equal to the area of a parallelogram with sides PQ and PR. The area of the triangle PQR is half of the area of the parallelogram.
  • #1
SigmaCrisis
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I'm given three points in 3D space (vectors), P, Q, and R. So I have to find a vector that is perpendicular to the plane formed by these points.

Anyone? Thanks.

I really just need some hint(s) for this.
 
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  • #2
Draw two vectors from any of the points to other points. Only one plane defines those two vectors. The cross product of those two vectors is an orthogonal vector to that plane.
 
  • #3
Umm, sorry, but could you elaborate? I don't quite get it...new to Calc III.
 
  • #4
if p,q are two points, subtracting Q-P gives a vector pointing from P to Q.

Thus if P,Q,R are 3 points, spanning a plane, the two vectors Q-P and Q-R are both parellel to that plane.


then there is a construction called cross product for finding sa vector perpendiculr to two given vectors. hence perpendiculr to the plane they are parallel to.

thus (Q-P) x (Q-R) is perpendicualr to the plane spanned by P,Q,R.
 
  • #5
Thanks a bunch!
 
  • #6
One more thing, I'm also asked to find the area of the triangle PQR.
 
  • #7
Think about the magnitude of the cross product. What is the relationship to the area of a parallelogram with two sides (PQ and PR) given by the vectors?

Then what is the relationship of the area of the parallelogram to the triangle formed by the two sides, e.g. PQ, PR and the third QR?
 
  • #8
Thanks a lot.
 

1. What is a vector?

A vector is a mathematical quantity that has both magnitude (size) and direction. It is often represented by an arrow with its length representing its magnitude and its direction indicating the direction of the vector.

2. How are vectors typically written?

Vectors are typically written using bold letters, such as v, or with an arrow on top, such as →v. They can also be written as a column matrix with the components listed vertically, such as [vx, vy, vz].

3. What is a cross product?

A cross product is a mathematical operation that produces a vector which is perpendicular to both of the vectors being multiplied. It is denoted by the symbol × and is only defined in three-dimensional space.

4. How do you calculate the cross product of two vectors?

The cross product of two vectors a and b can be calculated using the following formula: a × b = [aybz - azby, azbx - axbz, axby - aybx]. This will result in a vector that is perpendicular to both a and b.

5. What are some applications of vectors and cross products?

Vectors and cross products have various applications in science and engineering. They are commonly used in physics to represent forces and velocities, in engineering for structural analysis and mechanics, and in computer graphics for 3D transformations and animations. They are also used in many other fields, such as navigation, robotics, and even biology.

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