couple here to help please:

a) if position vector A has co-ordinates (2, -1) how do I calculate the unit vector in the direction OA where O is the origin? Is it 2v?

b) If I have 3 vectors P, Q, and R all with 3D co-ordinates how do write the sum t down of all 3?

c) How do I find the cosine of the angle between t and r?

Cheers