# Product of 2 vectors help

1. May 13, 2008

### gtfitzpatrick

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

r.k where r=xi+yj+zk

3. The attempt at a solution

is the answer to this just z or is it x+y

2. May 13, 2008

### cristo

Staff Emeritus
Well, why do you think it is either of the answers you quote?

What is the definition of the dot product of two vectors?

3. May 13, 2008

### gtfitzpatrick

Dot product of 2 vectors a.b is a1b1+a2b2+a3c3?

4. May 13, 2008

### gtfitzpatrick

i think k.k = 0

5. May 13, 2008

### cristo

Staff Emeritus
Ok, good. So, presumably, this definition is for two vectors a=(a1,a2,a3) and b=(b1,b2,b3). Can you write your two vectors in this form?

Hold on.. this doesn't agree with what you stated above. Have another think...

6. May 13, 2008

### gtfitzpatrick

xi+yj+zk.k so this is x0+y0+z1 = z?

7. May 13, 2008

### cristo

Staff Emeritus
Yup, that's correct.

8. May 13, 2008

### gtfitzpatrick

thanks a mill

9. May 13, 2008

### cristo

Staff Emeritus
No problem!