I have a problem about vectors.
When 3 coordinates of A, B, and C form a triangle in a 3D, the sum of $(\vec {AB}+\vec {BC}+\vec {CA}=\vec 0)$ is always zero. Then when the $\vec {AB}$ x $\vec {BC}$, it is equal to $\vec {BC}$ x $\vec {CA}$ and $\vec {CA}$ x $\vec {AB}$. Why does this happen?
Thank you