Даны векторы a (2;3) и n (-1;1/2).
cos(a∧n) = (2*(-1)+3*(1/2)) / (√(2²+3²)*√((-1)²+(1/2)²) =
= (-2+(3/2)) / (√4+9)*√(1+(1/4)) = (-1/2) / (√13*√(5/4)) ≈
≈ -0,5 / ( 3,605551 *
1,118034) ≈
-0,12403.
Угол равен arc cos (-0.12403) = 1,695151 радиан = 97,12502°.