Introduction:
When two unit vectors are added together, their sum may or may not be a unit vector depending on their magnitudes and directions. In this case, we assume that the sum of the two unit vectors is also a unit vector. We need to find the magnitude of their difference and the angle between them.

Solution:
Let's consider two unit vectors, A and B, and their sum C. We can represent these vectors in terms of their components:

A = (a1, a2, a3)
B = (b1, b2, b3)
C = (c1, c2, c3)

Step 1: Finding the sum of two unit vectors:
To find the sum of A and B, we add their respective components:

C = A + B
C = (a1 + b1, a2 + b2, a3 + b3)

Since C is also a unit vector, its magnitude must be equal to 1:

|C| = √(c1^2 + c2^2 + c3^2) = 1

Step 2: Finding the magnitude of their difference:
The difference between two vectors can be found by subtracting their respective components:

D = A - B
D = (a1 - b1, a2 - b2, a3 - b3)

To find the magnitude of D, we calculate its length:

|D| = √((a1 - b1)^2 + (a2 - b2)^2 + (a3 - b3)^2)

Step 3: Finding the angle between the vectors:
To find the angle between two vectors, we can use the dot product formula:

A · B = |A| |B| cos(θ)

Since A and B are unit vectors, their magnitudes are both 1:

1 · 1 = cos(θ)

So, θ = arccos(1) = 0 degrees

Conclusion:
If the sum of two unit vectors is also a unit vector, the magnitude of their difference will depend on the specific values of their components. The angle between them will always be 0 degrees, indicating that they are parallel.