Question

if the sum of two unit vectors is a unit vector then the magnitude of their difference is

Answer 1

As question said.... Sum of 2 unit vector is a unit vector.. 

Lets call these 2 unit vectors as A and B vector. 
This means, 
magnitude of A=1magnitude of B=1magnitude of A+B=1Now as you may recall the formula we studied...
magnitude of (A+B)= sqrt(A2+B2+2ABcos(x))
Here x represents the angle between 2 vectors (A and B) 
Now plugging the values as 
A=1
B=1
And A+B=1
We can get cos (x) =-0.5
And this means x=120 degrees
Once part of the question over...