Find the value of $(r_1-r)(r_2-r_3)$

Question

$$=(\frac {\Delta}{s-a}-\frac{\Delta}{s})(\frac{\Delta}{s-b}-\frac{\Delta}{s-c})$$ $$=\Delta ^2(a)(b-c)\frac {1}{\Delta ^2}$$ $$a(b-c)$$

But the answer given is $a^2$

$r_1,r_2, r_3$ are the ex radii on sides a, b and c respectively.