# The dot product.

1. Nov 24, 2004

### Matt2k

I'm sorry if this is placed under the wrong section of the forum.

But i really need help with a problem.

Well, here it is;

Find a unit vector that is parallel to the xy-plane and perpendicular to the vector 4i - 3j + k *note* there is a ^ above the ijk.

2. Nov 24, 2004

### Hurkyl

Staff Emeritus
Can you write down an algebraic condition for a vector to be parallel to the xy plane?
What about for a vector to be perpendicular to 4i-3j+k?
And for a vector to be a unit vector?

3. Nov 25, 2004

### BobG

If the vector is parallel to the xy plane, it must be perpendicular to the z-axis. Unit vector k lies on the z-axis. So, if you find a vector that's perpendicular to both unit vector k and your vector, it will solve your problem.

Whenever you take the cross product of two vectors, the result is perpendicular to both of the original vectors.