# Vector Cross Product

1. Dec 11, 2011

### hatchelhoff

I am trying to figure out the following
If R2 = 1.043j -1.143k
Then how can
R2 = 1.547

2. Dec 11, 2011

### Fredrik

Staff Emeritus
A vector can't be equal to a number. However, $\vec R_2=1.043\vec j-1.143\vec k$ implies that $|\vec R_2|\approx 1.547$. This follows immediately from the definition of $|\vec x|$ for arbitrary $\vec x$, or if you prefer, from the Pythagorean theorem. It doesn't have anything to do with the cross product.

3. Dec 11, 2011

### S_Happens

Not that there is anything wrong with Fredrik's post above, but my guess is that if you (the OP) don't know what's going on in your own post, then you won't understand the reply.

Fredrik used correct notation to show when talking about a vector and when talking about the magnitude of a vector. Your first mention of R2 is close to being in unit vector notation (without the overhead arrows or crowns or whatever convention). The second time you are simply stating the magnitude of the vector R2.

The magnitude of the vector is the square root of the squares of the magnitudes of the components. Nothing you have posted has anything to do with a cross product, which is an operation on two vectors.

4. Dec 11, 2011