If $a$ and $b$ are adjacent sides of a rhombus,then

In a parallelogram $ABCD$,if the diagonals are $\overline{AC}$ and $\overline{BD}$,then $\overline{AC} - \overline{BD} = \dots$

Answer the following as true or false.
Two collinear vectors are always equal in magnitude.

If $\overline{OA} = 3\hat{i} + \hat{j} - \hat{k}$,$|\overline{AB}| = 2\sqrt{6}$ and the direction ratios of $\overline{AB}$ are $1, -1, 2$,then $|\overline{OB}| = $

If $ABCDEF$ is a regular hexagon,then $\overrightarrow {AD} + \overrightarrow {EB} + \overrightarrow {FC} = $

If the position vectors of points $A$ and $B$ are $2\hat{i} + 3\hat{j} + 4\hat{k}$ and $3\hat{i} - 4\hat{j} - 5\hat{k}$ respectively,find $\overline{AB}$.