Question

if sum of two unit vectors is also a unit vector, then magnitude of their difference and angle between the two given unit vectors is

Answer 1

Sum of two vectors means resultant oftwo vectors . If we do apply a vectorequal in magnitude but opposite to the resultant then the three vectors ( leaving the resultant ) will be in equilibrium . Obviously the the threevectors are equal in magnitude and are at an angle of 120 degree to each other .
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