Given the vertices of a triangle are \( A(1, -1, -3) \), \( B(2, 1, -2) \), and \( C(-5, 2, -6) \). Compute the length of the bisector of the interior angle at vertex A.
Show Hint
For finding the angle bisector length in 3D, use the general formula for bisectors in triangles with known side lengths.
The formula for the length of the angle bisector is:
\[
l = \sqrt{bc \left( 1 - \frac{a^2}{(b+c)^2} \right)}
\]
where \( a \), \( b \), and \( c \) are the sides of the triangle.
After computing the side lengths and substituting into the formula, we find that the length of the bisector is \( 3 \sqrt{10} \).