# Thread: Finding angle between two unit vectors

1. ## Finding angle between two unit vectors

Hello

Given two unit vectors A,B and their sum (vector C) which is also a unit vector, find the angle between B and C?

2. When working with vectors, you usually compute the angle by
$
cos \theta = \frac {\vec A \cdot \vec B}
{ A B }
$

where the denominators refer to the magnitude of the vectors.

In this case, since C = A + B is also a unit vector, are you working with an equilateral triangle?

3. Thats what I thought and therefore wouldnt the answer be 60 degrees. But talking to my friend, she was arguing the answer is 120 degrees.

4. Originally Posted by Martin Billado
Thats what I thought and therefore wouldnt the answer be 60 degrees. But talking to my friend, she was arguing the answer is 120 degrees.
Unless the two vectors are perpendicular, there is obviously both an acute angle and an obtuse angle between them ....