I tried gooogling how to do it but there were none that could relate to the problem I have. 

Find the angle bisectors of the lines:
$$g: r=
 \begin{pmatrix}
 2 \\
 5 \\
 -9 \\
 \end{pmatrix}+u \begin{pmatrix}
 8 \\
 4 \\
 1 \\
 \end{pmatrix}
$$

$$f: r=
 \begin{pmatrix}
 2 \\
 5 \\
 -9 \\
 \end{pmatrix}+v \begin{pmatrix}
 12 \\
 4 \\
 3 \\
 \end{pmatrix}
$$

Could someone give me an idea on how to start solving this question?
I know that in order to determine the direction of the angle bisectors of the lines need to have the same length. So if

$u$ or $v$ =$0$
then they would have the same length no? But idk how to go from there.