In a $\triangle A B C$, if $(a-b)(s-c)=(b-c)(s-a)$, then $r_1+r_3=$

In $\triangle ABC$, $\cos A + \cos B + \cos C = $

In a $\triangle A B C$, if $a=26, b=30, \cos c=\frac{63}{65}$, then $c=$

If $H$ is orthocentre of $\triangle A B C$ and $A H=x ; B H=y$; $C H=z$, then $\frac{a b c}{x y z}=$