I'm trying to use vector dot product to get the angle between two vectors, but I'm puzzled by the results.

Given two vectors, A and B:

A(0.0, 0.2, 0.0)

B(0.8, 0.0, 0.0)

The angle between those, calculated with the dot product:

alpha= (acos(A*B)) * RAD_TO_DEG

properly returns 90°.

Now, let's have two vectors pointing in the same direction:

A(0.2, 0.2, 0.0)

B(0.8, 0.8, 0.0)

Would you guys explain me why in this case alpha is equal to 9.9°, while I'd expect to return 0°? Thanks