# Homework Help: Cross Product Directions

1. Oct 19, 2007

### Ryo124

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

Sketch a 3-dimensional picture showing the horizontal plane, a point P on the plane, a vertical line through P, and three vectors at P: vector A points vertically upward; vector B points toward the east; vector C points toward the south.

Now determine the cross product directions.
A x C
A x B
B x C
B x A

You have choices of: up, down, north, south, east, and west.

2. Relevant equations

??

3. The attempt at a solution

2. Oct 19, 2007

### mdk31

Have you learned the right hand rule?

3. Oct 21, 2007

### Ryo124

As I said, I have no idea on how to solve this problem.

I know the right hand rule, but I thought that it was only for currents, directions of B fields, and the direction of the magnetic force.

4. Oct 21, 2007

### mdk31

The right hand rule also applies to the cross product of vectors.

http://mathworld.wolfram.com/Right-HandRule.html

"The right-hand rule states that the orientation of the vectors' cross product is determined by placing u and v tail-to-tail, flattening the right hand, extending it in the direction of u , and then curling the fingers in the direction that the angle v makes with u . The thumb then points in the direction of u x v."

5. Oct 21, 2007

### Ryo124

Thanks man. I was using my left hand....