Question

If the sum of two unit vectors is also a vector of 3 units magnitude, the magnitude of the difference of the two unit vectors is
A) 3 unit
B) 2 units
C) 1 units
D) Zero​

Answer 1

according to your question the magnitude of the vector difference comes out to be

$\sqrt{ - 5}$

which is generally not possible.

as you said that,

$|a + b| = 3$