For each statement, write down the converse. Determine which statements, and which of their converses, are true.

If $\mathrm{c}=9$, then ${\mathrm{c}}^2=81$.
 

For each statement, write down the converse. Determine which statements, and which of their converses, are true. 

If a right-angled triangle is drawn with its vertices on the circumference of a circle then its hypotenuse is a diameter of the circle.

In the cyclic quadrilateral $ABCD$, $\angle \mathrm{DAB}\cong \angle \mathrm{ABC}$. Prove that: $\mathrm{AD}=\mathrm{BC}$.

$A, B, C$ and $D$ lie on a circle center $O$, and $DOB$ bisects $\angle \mathrm{ABC}$. Prove that $△\mathrm{ABC}$, is isosceles.