공간벡터 사이 각

$\displaystyle \left| \vec{a} \right| = \sqrt{2 ^{2} + ( - 3 ) ^{2} + 2 ^{2}} = \sqrt{17}$ $\displaystyle \left| \vec{b} \right| = \sqrt{1 ^{} + ( - 4 ) ^{2} + 0} = \sqrt{17}$ $\vec{a} \cdot \vec{b} = 2 \cdot 1 + ( - 3 ) \cdot ( - 4 ) + 2 \cdot 0 = 14$ $\displaystyle \therefore \cos \theta = \frac{\vec{a} \cdot \vec{b}}{\left| \vec{a} \right| \left| \vec{b} \right|} = \frac{14}{\sqrt{17} \sqrt{17}} = \frac{14}{17}$