Algebraic Manipulation of Planar Vectors

It is given that \(A\) is the point \((3,4)\) and \(B\) is the point \((-5,1)\).

1. Find \(|\overrightarrow{AB}|\).
2. If \(\overrightarrow{CD} = \frac{1}{2}\overrightarrow{AB}\) and \(D\) is the point \((7,2)\), find the coordinates of the point \(C\).
3. If \(\overrightarrow{XY} = \begin{pmatrix} -2 \\ k \end{pmatrix}\) and \(\overrightarrow{XY}\) is parallel to \(\overrightarrow{AB}\), find the value of \(k\).