(b)
Let the coordinates of the third vertex $A$ be $(h,\ k)$
[image:10_image12.emf]
Also, $AD\bot BC$
$\therefore\frac{k - 0}{h - 0} \times \left( \frac{4}{- 7} \right) = - 1$
$\Rightarrow \ \ 7h = 4k$ …(i)
and $OB\bot AC$
$\Rightarrow \frac{k - 3}{h + 2} \times \left( - \frac{1}{5} \right) = - 1$
$\Rightarrow 5h - k + 13 = 0$ …(ii)
On solving Eqs. (i) and (ii), we get
Hence, the coordinates of third vertex are $( - 4,\ - 7)$