a) $\vecAB = (1,0,-2)$
$|\vecAB| = \sqrt1^2+0^2+(-2)^2=\sqrt5$
$\vecAC = (0,1,-3)$
$|\vecAC| = \sqrt0^2+1^2+(-3)^2=\sqrt10$ b) $\vecAB = (1,0,-2)$ , $\vecAC = (0,1,-3)$ , $\vecAD = (1,2,-1)$
$\left| \beginarrayccc 1 & 0 & 2 \ 0 & 1 & -3 \ 1 & 2 & -1 \endarray (…)