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

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