If $\Delta ABC \cong \Delta DEF$,and the area of $\Delta ABC$ is $58 \ cm^2$,then find the area of $\Delta DEF$ in $cm^2$.

In the figure,$D$ and $E$ are points on side $BC$ of a $\triangle ABC$ such that $BD = CE$ and $AD = AE$. Show that $\triangle ABD \cong \triangle ACE$.

For any convex quadrilateral $ABCD$,prove that $AB + BC + CD + DA < 2(AC + BD)$.

Prove that the sum of any two sides of a triangle is greater than twice the median with respect to the third side.

In the given figure,$PQ = PR$ and $\angle Q = \angle R$. Prove that $\triangle PQS \cong \triangle PRT$.

In $\triangle ABC$,$BC = AB$ and $\angle B = 80^{\circ}$. Then $\angle A$ is equal to: (in $^{\circ}$)