The formula is;
[tex]\begin{gathered} u.v=\lvert{u\lvert{}\rvert v}\rvert cos\theta \\ \end{gathered}[/tex][tex]\begin{gathered} u.v=5(4)+(-2)(6)+4(2) \\ u.v=16 \end{gathered}[/tex][tex]\begin{gathered} \lvert{u}\rvert=\sqrt{(5^2+-2^2+4^2)}\text{ } \\ \lvert{u=\sqrt{45}}\rvert \end{gathered}[/tex][tex]\begin{gathered} \lvert{v}\rvert=\sqrt{4^2+6^2+2^2} \\ \lvert{v}\rvert=\sqrt{56} \end{gathered}[/tex][tex]16=\sqrt{45}X\sqrt{56}\text{ }cos\theta\text{ }[/tex][tex]\cos\theta=\frac{16}{\sqrt{45}X\sqrt{56}}=\frac{16}{50.1996}=0.3187[/tex][tex]\theta=\cos^{-1}(0.3187)=\text{ 71}\degree[/tex]θ = 71°
