13 Line \(l _ { 1 }\) has equation
$$\frac { x - 2 } { 3 } = \frac { 1 - 2 y } { 4 } = - z$$
and line \(l _ { 2 }\) has equation
$$\mathbf { r } = \left[ \begin{array} { c }
- 7
4
- 2
\end{array} \right] + \mu \left[ \begin{array} { c }
12
a + 3
2 b
\end{array} \right]$$
13
- In the case when \(l _ { 1 }\) and \(l _ { 2 }\) are parallel, show that \(a = - 11\) and find the value of \(b\).
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