# Homework Help: Vector perpendicular to two vectors

1. Sep 11, 2011

### aigerimzh

1. The problem statement, all variables and given/known data
A=(i+j-k) B=(2i-j+3k)
Need to find vector perpenducilar to them

2. Relevant equations

3. The attempt at a solution
I've solved by finding A*B and then divided it to (A*B), the result was W=2i/$\sqrt{38}$-5j/$\sqrt{38}$-3k/$\sqrt{38}$. Is it correct?

Last edited: Sep 11, 2011
2. Sep 11, 2011

### HallsofIvy

What do you mean by A*B? I know scalar product, dot product, and cross product of vectors but none of those use "*". And what is the difference between "A*B" and "(A*B)"? If you mean |A*B|, the length of the vector, I see no reason to divide. The problem did not ask for a unit vector.

3. Sep 11, 2011

### aigerimzh

I mean AxB, and (AxB) means length of AxB. Do mean that my answer is not correct?

4. Sep 11, 2011

### HallsofIvy

No, I meant that I did not understand your answer. Yes, AxB is perpendicular to A and B and so satisfies the condition of the problem. And so AxB/|AxB| is a unit vector perpendicular to both A and B. But the problem did not ask for a unit vector.