Будет ли вектор c=3i-j перпендикулярен вектору d=2i+j-k
С=3i-j, c(3;-1;0) d=2i+j-k, d(2;1;-1) c_|_d, => cos( c d)=0 c*d=0. c*d=3*2+(-1)*1+0*(-1)=6-1=5 cos( c d)=5, => векторы с и d не перпендикулярны
![\frac{c*d}{|c|*|d|} =0, =\ \textgreater \](https://tex.z-dn.net/?f=+%5Cfrac%7Bc%2Ad%7D%7B%7Cc%7C%2A%7Cd%7C%7D+%3D0%2C+%3D%5C+%5Ctextgreater+%5C+ "\frac{c*d}{|c|*|d|} =0, =\ \textgreater \")