# Product of 2 vectors help

gtfitzpatrick

## Homework Statement

r.k where r=xi+yj+zk

## The Attempt at a Solution

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

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?

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

gtfitzpatrick
i think k.k = 0

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

i think k.k = 0
Hold on.. this doesn't agree with what you stated above. Have another think...

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

Staff Emeritus