Projections onto a plane and parallel to a vector

In summary, the conversation is about preparing for a Linear Algebra 1 exam and the difficulty in understanding projections. An example of a projection onto a plane is given, and the linear application P is defined. The person is struggling to understand how P is defined and how to define a projection in general. They also mention not understanding what it means for a projection to be "parallel to a vector" in this case. They express their appreciation for any help in understanding these concepts.
  • #1
Blacky&Imy
3
0
Hi. I'm preparing the Linear algebra 1 Exam for the first year of
Physics University. I find very difficult to understand projections.
Here's an example:
Consider the projection P: R^3 --> R^3 onto the plane U of equation
2x1 - 3x2 + x3 = 0 and parallel (the projection) to the vector v=(2,1,0).

This is to say, P is the linear application defined as follows:

P(x1,x2,x3) = ( -3x1 + 6x2 - 2x3 , -2x1 + 4x2 - x3 , x3 )

I can't see why P is defined this way, how they got it, so I would
appreciate if you could show me the passages step-by-step. In general, I can't understand how to define a projection, given the vector and the plane. Also, I'd
like to understand what does "parallel to a vector" means in this case.

Thanks a lot.
 
Physics news on Phys.org

1. What is the purpose of projecting a vector onto a plane?

The purpose of projecting a vector onto a plane is to find the component of the vector that lies in the same direction as the plane. This can be useful in various applications, such as solving physics problems or finding the shortest distance between a point and a plane.

2. How is the projection of a vector onto a plane calculated?

The projection of a vector onto a plane can be calculated using the dot product. The formula is: projvw = (w · u)u, where w is the vector being projected, v is a unit vector in the direction of the plane, and u is the normal vector of the plane.

3. What is the difference between projecting a vector onto a plane and parallel to a vector?

When projecting a vector onto a plane, the resulting projection vector is perpendicular to the plane. On the other hand, when projecting a vector parallel to another vector, the resulting projection vector is parallel to that vector.

4. Can a vector be projected onto a plane and parallel to a vector simultaneously?

No, a vector cannot be projected onto a plane and parallel to a vector at the same time. This is because the projection vector will either be perpendicular to the plane or parallel to the given vector, but not both.

5. What properties do the projection of a vector onto a plane and parallel to a vector have?

The projection of a vector onto a plane is always perpendicular to the plane, while the projection of a vector parallel to another vector is always parallel to that vector. Additionally, the magnitude of the projection vector is equal to the length of the original vector times the cosine of the angle between them.

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