The four points will be coplanar if the three vectors \(\overrightarrow{P_{1}
P_{2}}=\langle 3,-1,-1\rangle, \overrightarrow{P_{2}
P_{3}}=\langle-3,-5,13\rangle,\) and \(\overrightarrow{P_{3} P_{4}}=\)
\langle-8,7,-6\rangle are coplanar. \(\overrightarrow{P_{2} P_{3}} \times
\overrightarrow{P_{3} P_{4}}=\left|\begin{array}{ccc}\mathbf{i} & \mathbf{j} &
\mathbf{k} \\ -3 & -5 & 13 \\ -8 & 7 &
-6\end{array}\right|=\left|\begin{array}{cc}-5 & 13 \\ 7 &
-6\end{array}\right| \mathbf{i}-\left|\begin{array}{cc}-3 & 13 \\ -8 &
-6\end{array}\right| \mathbf{j}+\left|\begin{array}{cc}-3 & -5 \\ -8 &
7\end{array}\right| \mathbf{k}=\langle-61,-122,-61\rangle\)
\(\overrightarrow{P_{1} P_{2}} \cdot(\overrightarrow{P_{2} P_{3}} \times
\overrightarrow{P_{3} P_{4}})=\langle 3,-1,-1\rangle
\cdot\langle-61,-122,-61\rangle=-183+122+61=0\)
The four points are coplanar.