qu  =  (0.0, 1)T and ru  =  (0.5, 0.866)T ?

A good answer might be:

qu  · ru   =   cos θ   =  0.866.    So θ   =  arc cos 0.866  =  30°.

More Practice

 

The picture shows qu and ru and the angle between them.

Since qu · ru = ru · qu , the angle is the angle (< 180°) between the two vectors. It does not matter which vector is first in the dot product.

Sometimes (especially when vectors point into diferent quadrants) it really 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 qu  =  (0.0, 1)T and wu  =  (-0.5, 0.866)T ?