Find the difference between 2 unit vectors. The angle between them is 90 right? So 1+1-2cos90 should be 2 and thus the answer should be root 2, why do we find the angle to be 60 and then solve the Q?

Answer 1

Unit vectors are just that, vectors of magnitude 1 and not necessarily orthogonal. However if a and b are orthogonal then a-b cannot be found algebraicly and must be found as √a²+b²= √2 and angle is 90