In coordinate space, when the line passing through two points $\mathrm { A } ( 5,5 , a ) , \mathrm { B } ( 0,0,3 )$ is perpendicular to the line $x = 4 - y = z - 1$, what is the value of $a$? [3 points] (1) 3 (2) 5 (3) 7 (4) 9 (5) 11
In coordinate space, when the line passing through two points $\mathrm { A } ( 5,5 , a ) , \mathrm { B } ( 0,0,3 )$ is perpendicular to the line $x = 4 - y = z - 1$, what is the value of $a$? [3 points]\\
(1) 3\\
(2) 5\\
(3) 7\\
(4) 9\\
(5) 11