# Homework Help: Vectors and orthoganality

1. Oct 28, 2005

### nepenthe

orthogonal vectors

Hello..Can someone help me with the following question?

Let F,G, and Z be nonzero vectors, each orthogonal to other two..Let A be any vector.Show that there are unique scalars x,y, and z such that A=xF+yG+zH.

Thank You..

Last edited: Oct 28, 2005
2. Oct 28, 2005

### Physics Monkey

You want to write an arbitrary vector A in terms F, G, and H as A=xF+yG+zH.
If you can find a formula for x,y,z in terms of A, F, G, and H then you have solved your problem, right? Hint: think about the dot product.

3. Oct 29, 2005

### nepenthe

hello..I thought about using dot product.But I couldn't apply to this problem..and I think the main problem is that I can't imagine this question in my head..
could you please give me the solution(just to understand the the process)..and also solution methods for these "show that or prove that" questions..what is the first thing that I have to think?

Thankk you..

4. Oct 29, 2005

### HallsofIvy

You "thought" about using the dot product? Why not just use it?

Do you know what "orthogonal" means? I suggest you look it up.

5. Oct 29, 2005

### nepenthe

First, because I couldn't solve this ploblem, I am here..

I know what orthogonal means..I wrote equations for dot product..But I have no idea how to show there are unique scalars? or why there are unique scalars x,y, and z??

6. Oct 29, 2005

### HallsofIvy

DO IT!!!
The best way to prove something exists is to show how to find it.
If A= xF+yG+zH, what is the dot product of both sides with F? Can you solve that equation for x?