Three points A (0,1, -1), B (1, -1,2), C (3,1,0) are given. Indicate equal vectors among the vectors AB, BC, AC and BA.

Find the length of each of the listed vectors
| AB | = √ ((xa + xb) ^ 2 + (ya + yb) ^ 2 + (za + zb) ^ 2)
| AB | = √ (1 + 1) = √2
AB = BA = √2
| BC | = √ ((xb + xc) ^ 2 + (yb + yc) ^ 2 + (zb + zc) ^ 2)
| BC | = √ (16 + 4) = 2√5
| AC | = √ ((xa + xc) ^ 2 + (ya + yc) ^ 2 + (za + zc) ^ 2)
| AC | = √ (9 + 4 + 1) = √14
Answer: only vectors AB and BA are equal