If your viewpoint changes,
do the angles between the 3D edges of the box change?

# Angles between Coordinate Axes

The angle between two vectors in 3D depends on their relation
to each other (and does not depend on your viewpoint, or the
coordinate frame you are using).
Of course,
when a 2D picture shows a 3D scene the angles in the picture
very much depend on the viewpoint.

In the previous chapter you saw a formula for the angle
θ
between two unit vectors:

**a**_{u} · b_{u} = cos θ

### QUESTION 3:

Apply this formula to the two unit vectors
parallel to the x axis and y axis:
(1,0,0)^{T} and (0,1,0)^{T}.