Define opposite vertices of a quadrilateral.

A circle is inscribed in quadrilateral ABCD, touching sides AB, BC, CD and DA at P, Q,R and S, respectively. If $\mathrm{As}=6\mathrm{cm},$ $\mathrm{BC}=12\mathrm{cm}$ and $\mathrm{CR}=5\mathrm{cm}$, then the length of AB (in cm) is

Identify whether the following polygon is a quadrilateral or not$?$

State True or False:

A square is a regular quadrilateral.

Identify whether the following polygon is a quadrilateral or not$?$