Font TeX:

\cos \left( \alpha \right)= \frac{1 \cdot 2+4 \cdot \left(-6\right)}{\left|u\right| \cdot \left|v\right|} = \frac{-22}{ \sqrt{1^{2}+4^{2}} \cdot \sqrt{2^{2}+\left(-6\right)^{2}} } = \frac{-22}{ \sqrt{17} \cdot \sqrt{40} }=-0,84