How do you determine whether u and v are orthogonal, parallel or neither given #u=2i-2j# and #v=-i-j#?
u is not a scalar multiple of v. So, they are not parallel, The scalar product
The scalar product
So, cosine of the angle = 0. And so, the vectors are orthogonal.
If the vectors are parallel, they will be of the form <x, y> and k<x, y>,