From part (a) we know that the direction vector of the line L {\displaystyle \displaystyle L} is ( 1 − 5 − 3 ) {\displaystyle \displaystyle {\begin{pmatrix}1\\-5\\-3\end{pmatrix}}}
L = Q + t ( 1 − 5 − 3 ) = ( a b c ) + t ( 1 − 5 − 3 ) {\displaystyle \displaystyle L=Q+t{\begin{pmatrix}1\\-5\\-3\end{pmatrix}}={\begin{pmatrix}a\\b\\c\end{pmatrix}}+t{\begin{pmatrix}1\\-5\\-3\end{pmatrix}}}
