⇒
[m]\vec{d}=(3 λ ;-6 λ ;-3 λ )[/m]
[m]\vec{d}\cdot \vec{c}=3 λ\cdot 0+(-6 λ)\cdot (-1)+(-3 λ )\cdot 3=6 λ-9 λ =-3 λ [/m]
[m]\vec{d}\cdot \vec{c}=15 [/m]
⇒
[m]-3 λ =15 [/m]
[m] λ =-5 [/m]
[m]\vec{d}=(3\cdot (-5) ;-6 \cdot (-5) ;-3\cdot (-5) )=(-15;30;15)[/m]