# More Practice

The picture shows **q**_{u} and **r**_{u} and the
angle between them.

Recall that **q**_{u} · r_{u} =
**r**_{u} · q_{u} .
The angle between the two vectors must be 180° or less (by definition).
It does not matter which vector is first in the dot product.

Sometimes (especially when vectors point into different quadrants) it
helps
to draw a picture to check that your answer makes sense.

### QUESTION 9:

What is the cosine of the angle between the two unit vectors
represented by
**q**_{u} = (0.0, 1)^{T}
and
**w**_{u} = (-0.5, 0.866)^{T} ?