cosa=[-2,5*(-5)+2,5*5+0*5sqrt(2)]/sqrt(2,5^2+0^2+(-2,5)^2) * sqrt(5^2+(-5)^2+5sqrt(2)^2))=
=25/sqrt(12,5*100)=25/sqrt(1250)=1/sqrt(2)=sqr(2)/2
a=П/4
cosa=[-2,5*(-5)+2,5*5+0*5sqrt(2)]/sqrt(2,5^2+0^2+(-2,5)^2) * sqrt(5^2+(-5)^2+5sqrt(2)^2))=
=25/sqrt(12,5*100)=25/sqrt(1250)=1/sqrt(2)=sqr(2)/2
a=П/4