Vectors - Angle Between Two Planes

\(2\) Intersecting Planes
☐ Equation of intersecting line without using GC
☐ Equation of intersecting line by using GC
☐ Angle between the planes

The planes \({{\mathrm{p}}_{1}}\) and \({{\mathrm{p}}_{2}}\) have equations \(\mathbf{r}\cdot \left( \begin{matrix}1  \\ -3  \\  2  \end{matrix} \right)=-5\) and \(\mathbf{r}\cdot \left( \begin{matrix}  2  \\-1  \\  3  \end{matrix} \right)=1\) respectively, and meet in the line \({{l}_{4}}\). Find

1. the vector equation for \({{l}_{4}}\),
2. Find the acute angle between \({{\mathrm{p}}_{1}}\) and \({{\mathrm{p}}_{2}}\).