## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

When two vectors $u$ and $v$ are orthogonal, then the angle between these two vectors is given by $90^\circ$. Thus, we have: $||u\times v||=||u||\ ||v||\sin{\theta}\\=||u||\ ||v||\sin{90^\circ}\\=||u||\ ||v|| \ (1)\\=||u|| \ ||v||$