\mathrm{arc} \cos \frac{\left| \, \mathbf{u} \cdot \mathbf{v} \, \right|}{\left| \, \mathbf{u} \, \right| </p> <pre> \cdot \left|  \, \mathbf{v}  \, \right|} =  \mathrm{arc} \cos  \frac{\left| \,    \left( \, =       1, \,  -1, \, 2  \, \right) \cdot \left(  \, 3, \,  6, \, 3 \,  \right) \,  \right|}{\sqrt{1^2 + \left( \, -1 \,  \right)^2 + 2^2} \cdot \sqrt{3^2 + 6^2 +    3^2}} = \mathrm{arc} \cos \frac{1}{6} = 1.40 \text{ radianes} </pre> <p>
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