Angle Between Vectors in Terms of Dot Product

Theorem
The angle between two non-zero vector quantities can be calculated by:
 * $\theta = \arccos \frac {\mathbf v \cdot \mathbf w} {\norm {\mathbf v} \norm {\mathbf w} }$

where:
 * $\mathbf v \cdot \mathbf w$ represents the dot product of $\mathbf v$ and $\mathbf w$
 * $\norm {\, \cdot \,}$ represents vector length
 * $\arccos$ represents arccosine.

Also see

 * Angle Between Non-Zero Vectors Always Defined