a{-4;1;1} и b{-1;-1;0}
ab=4-1+0 =3
|a| = √( 16+1+1)=√18 =3√2
|b| = √(1+1+0) = √2
cosa=3/3√2 * √2 =1/2
a=+- π/3+2πn
