# Homework Help: [Dot Product] Vector Proection

1. Nov 3, 2011

### Highway

[Dot Product] Vector Projection

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

I am not sure what to do here -- I know that the projection of u onto a "dotted" with w = 0 by definition, but I don't know how to show this.

added this second part after plugging in for the definition of the projection we derived in class, then simplified. . .

Last edited: Nov 3, 2011
2. Nov 3, 2011

anyone?

3. Nov 3, 2011

### I like Serena

Hi Highway!

You have an expression for the projection.
Can you substitute that (and only that) in the formula you have for w?

To show that 2 vectors are orthogonal, you need to show that their dot product is zero. That is, that $\vec a \cdot \vec w = 0$.

What you need to know, is that there are calculation rules for dot products.
For instance $\vec a \cdot (\vec b+\vec c) = \vec a \cdot \vec b + \vec a \cdot \vec c$.

Can you simplify the expression for $\vec a \cdot \vec w = 0$?

4. Nov 3, 2011

### Highway

Thanks!! I got it figured out :P

5. Nov 3, 2011

Congrats!