252

a)
$\overline{BC}=\overline{AD}$
$\overline{BC}=4\overline{\text{i}}+2\overline{\text{j}}+5\overline{\text{k}}$
$\overline{OD}=\overline{OA}+\overline{AD}=-2\overline{\text{i}}+\overline{\text{j}}+3\overline{\text{k}}+4\overline{\text{i}}+2\overline{\text{j}}+5\overline{\text{k}}=2\overline{\text{i}}+3\overline{\text{j}}+8\overline{\text{k}}$
$D=\left(2{,}\ 3{,}\ 8\right)$
b)