(c)
Let the position of $B$ is $\overrightarrow{\mathbf{r}}$.
$\therefore\ \overrightarrow{\mathbf{a}} = \frac{2\overrightarrow{\mathbf{r}} + 3(\overrightarrow{\mathbf{a}} + 2\overrightarrow{\mathbf{b}})}{2 + 3}$
[image:10_image6.emf]
$\Rightarrow 5\overrightarrow{\mathbf{a}} = 2\overrightarrow{\mathbf{r}} + 3\overrightarrow{\mathbf{a}} + 6\overrightarrow{\mathbf{b}}$
$\Rightarrow \ 2\overrightarrow{\mathbf{r}} = 2\overrightarrow{\mathbf{a}} - 6\overrightarrow{\mathbf{b}}$
$\therefore\ \overrightarrow{\mathbf{r}} = \overrightarrow{\mathbf{a}} - 3\overrightarrow{\mathbf{b}}$