Question

найдите угол между векторами a= {0; -1; -1) b= {-1; 0; 1)

Answer 1

cosu=(x1•x2+y1•y2+z1•Z2)/|a|•|b|=
-1/(√2•√2)=-1/2
u=120°

Answer 2

$cos{\alpha }=\frac{\vec{a}*\vec{b}}{|\vec{a}|*|\vec{b}|} =\frac{-1*0-1*0-1*1}{\sqrt{0^2+(-1)^2+(-1)^2}*\sqrt{(-1)^2+0^2 +1^2}} =\frac{-1}{\sqrt{2}*\sqrt{2}} =-\frac{1}{2} \\ \\ \\ \alpha=\frac{2\pi}{3} \\ \\ OTBET: \ \alpha=\frac{2\pi}{3}$