6 The equations of two non-intersecting lines, \(l _ { 1 }\) and \(l _ { 2 }\), are
\(l _ { 1 } : \mathbf { r } = \left( \begin{array} { c } 1
2
- 1 \end{array} \right) + \lambda \left( \begin{array} { c } 2
1
- 2 \end{array} \right) , \quad l _ { 2 } : \mathbf { r } = \left( \begin{array} { c } 2
2
- 3 \end{array} \right) + \mu \left( \begin{array} { c } 1
- 1
4 \end{array} \right)\).
Find the shortest distance between lines \(l _ { 1 }\) and \(l _ { 2 }\).