# The Cross Product

1. Dec 20, 2014

When we talk about the angle between two vectors while computing the cross product, which angle are we referring to exactly? According to most sources, the angle should be between 0 and π; yet according to my math book, "the angle is measured in an anticlockwise sense from a to b, if the vector product a x b is to be computed."

2. Dec 20, 2014

### SteamKing

Staff Emeritus

http://www.mathsisfun.com/algebra/vectors-cross-product.html

Scroll down a ways to see the diagram of the angle.

3. Dec 20, 2014

### Matterwave

The trigonometric function occurring in the cross product is sine. Notice that sin(360-x)=sin(-x)=-sin(x) so notice that the only thing that changes whether you measure the small angle or the big angle is that you change the sign. For that issue, just follow the right hand rule. :)

4. Dec 20, 2014

$$a\times b=-b\times a$$