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

### Answer:

Again, cos x = 0.866. So it must be that x = arc cos 0.866 = 30°.

# Which Side?

Both vectors **r**_{u} and **w**_{u} gave the
answer cos 30,
when the dot product was done with **q**_{u},
although they lie on either side of **q**_{u}.

In two dimensions, there are two unit vectors that are 30°
away from a given vector.
Both of them will give you the same dot product with the given vector.
Be careful to draw a picture in ambiguous situations.

### QUESTION 10:

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