If in $\Delta ABC, AC > AB > BC$,then find the greatest angle of the triangle.

Prove that if in two triangles,two angles and the included side of one triangle are equal to two angles and the included side of the other triangle,then the two triangles are congruent.

Bisectors of the angles $B$ and $C$ of an isosceles triangle with $AB = AC$ intersect each other at $O$. $BO$ is produced to a point $M$. Prove that $\angle MOC = \angle ABC$.

In $\Delta PQR$,$PQ = PR$. Prove that $\angle R = \angle Q$.

$Q$ is a point on the side $SR$ of a $\triangle PSR$ such that $PQ = PR$. Prove that $PS > PQ$.

In $\Delta PQR$,$PQ = 7.5 \, cm$,$QR = 6.2 \, cm$ and $a < PR < b$,then find the values of $a$ and $b$ in $cm$.