Math Help - Help with calculation of a Matrix

1. Help with calculation of a Matrix

Hey

I'm stuck at a question here and I am not really sure how to go about it. If someone could give me some guidance I would appreciate it.

Okay so here's the question:

Calculate the matrix $A^{10}$ if A is the matrix for the representation/image that is the orthogonal projection on the plane $2x - y + 25z = 0$.

Sorry if my translation is a bit confusing. If it is I could try and clarify but for a better lack of words this is what I got out from it. What I need is to find out the value of matrix A. If I get that I am sure I can solve it on my own.

2. I think that may be this is in mind:
find projection of any point P to point Q which is in this plane
such as
A P = Q .

3. I'm not sure I follow you there. With the information given I need to find out the value of matrix A, from there I can diagonalize it. But how would I get the value of matrix A? The question also hinted that one could easily take out two vectors from the plane, yeah sure that's easy. Both with the eigenvalue of 1. But I am still stuck.

Any guidance?