# Find unit vetors satisfying qualifying conditions HELP test tomorrow

1. Oct 26, 2008

### darthxepher

Find unit vetors satisfying qualifying conditions!!! HELP test tomorrow

1. The problem statement, all variables and given/known data
Find the unit vectors satisfying qualifying conditions:

a. oppositely directed to 3i-4j

b. same direction as 2i-j-2k

c. same direction as vector from A(-3,2) to B(1,-1)

Thoughts.
Ok. So i don't know where to start. Can someone hint me. I know to find unit vector u must divide each term by the magnitude but the direction stuff isn't helping me. lol

2. Oct 26, 2008

### gabbagabbahey

Re: Find unit vetors satisfying qualifying conditions!!! HELP test tomorrow

Call the unit vector $\hat{n}=n_1\hat{i}+n_2\hat{j}+n_3\hat{k}$ and look at what your conditions tell you about $\hat{n}$...

(a) directed oppositely to 3i-4j....what is the direction of 3i-4j...what does that mean the direction of $\hat{n}$ is?...remember $\hat{n}$ is a unit vector, so you know its magnitude is 1.

(b)same direction as 2i-j-2k...what IS the direction of 2i-j-2k?

(c)what is the vector from A to B?...what is its direction?

3. Oct 26, 2008

### darthxepher

Re: Find unit vetors satisfying qualifying conditions!!! HELP test tomorrow

Ok. I kinda figured it out. Thanks for the help... But can u check ur answers with me.

a) (-3/5)i + (4/5)j

b) (2/3)i - (1/3)j - (2/3)k

c) (4/5)i - (3/5)j