Now, cos θ = -0.866. So θ = arc cos -0.866 = 150°.

q_{u} = (0.0, 1)^{T} and z_{u} = (-0.5, -0.866)^{T}

The angle between the two vectors is greater than 90°, so the cosine is negative.

In the diagram above, mentally draw the other vector that has a dot product of -0.866 with vector q_{u}.