For any line of the form a + t v {\displaystyle a+t{\textbf {v}}} , the vector v {\displaystyle {\textbf {v}}} gives the direction of the line.
Therefore, the direction vector of the line L 1 {\displaystyle L_{1}} is [ − 1 , 2 , 2 ] {\displaystyle [-1,2,2]} .