Problem:
Find the angle between the following two vectors:
$\left(
\begin{array}{c}
 0 \\
 0 \\
 0 \\
 -1 \\
 1 \\
 0 \\
\end{array}
\right)$ and
$\left(
\begin{array}{c}
 1 \\
 -1 \\
 -1 \\
 1 \\
 0 \\
 -1 \\
\end{array}
\right)$.
Answer:
$\frac{\pi }{2}+\cot ^{-1}(3)$
{'source': 'AMPS', 'file': 'amps/mathematica/linear_algebra/vector_angles_and_projections/13122.txt'}