Understanding the Right Hand Rule: Determining Direction Using Cross-Products

[Tiven white]

Homework Statement

If z is east and y is north then x is?
A. West
B. East
C. North
D. South
E. Down

Homework Equations

I have trued getting the proper orientation but the direction I would have obtained is not an option 'up' a comment would be appreciated

The Attempt at a Solution

 

[voko]

Obviously, it can be either up or down. Assuming one of the given answers must be correct, that must be "down".

To see that, you would need to twist your arm quite severely. Align your middle finger (Z) with East and your index finger with South. Then your thumb will be Up. Now to make your index index finger point North as described, you would need to rotate your hand about your middle finger.

 

[rude man]

You did not define the equation for the cross-product vector x.

If x = y x z then x is down.
If x = z x y then x is up.

EDIT: OK, never mind, you did not have "up" as one of your choices. So voko answered the question.