The angle between two vectors a and b is ∅, where ∅≠90°. Under what conditions will |Projab|2 + |Projba|2 = 1?
Don't really know where to start on this one.
I'm not entirely sure what you mean with Projab.
Presumably it is:
where is the unit vector in the direction of .
If that is the case you can substitute .
And you can substitute something similar for the other projection.
Have you tried that?
If so, what did you get?