Problem:
Find the angle between the following two vectors:
$\left(
\begin{array}{c}
 -8 \\
 4 \\
 4 \\
 -4 \\
 -9 \\
\end{array}
\right)$ and
$\left(
\begin{array}{c}
 -3 \\
 3 \\
 -3 \\
 4 \\
 -4 \\
\end{array}
\right)$.
Answer:
$\cos ^{-1}\left(\frac{44}{\sqrt{11387}}\right)$
{'source': 'AMPS', 'file': 'amps/mathematica/linear_algebra/vector_angles_and_projections/22129.txt'}