In triangle $ABC$, if $a=7, b=10, c=11$, then $\frac{R}{r}=$

In $\triangle ABC$,find the value of $\frac{r_1-r}{a}+\frac{r_2-r}{b}$.

In $\triangle ABC$,what is the value of $r_1+r_2+r_3-r$?

If $I$ is the incentre of $\triangle ABC$ and $P_1, P_2, P_3$ are respectively the radii of the circumcircles of the $\triangle IBC, \triangle ICA$ and $\triangle IAB$,then $P_1 P_2 P_3=$

In $\triangle ABC$,if $a=8, b=10, c=12$,then $\frac{r}{R}=$

In $\triangle ABC$, if $a : b : c = 4 : 5 : 6$, then the ratio of the circumradius to its inradius is