In $\triangle A B C, r_1 \cot \frac{A}{2}+r_2 \cot \frac{B}{2}+m_3 \cot \frac{C}{2}=$

In $\triangle A B C, b c-r_2 r_3=$

If $O(0,0,0), A(3,0,0)$ and $B(0,4,0)$ form a triangle, then the incentre of $\triangle O A B$ is

In $\triangle A B C$, if $r_1=4, r_2=8$ and $r_3=24$, then $a=$