Construct a regular hexagon of side $4.1 \mathrm{cm}$.

In the given figure, $ABCD$ is a rhombus whose diagonals intersect at $O$. If $\angle OAB:\angle OBA=2:3$ . Find  the angles of $△OAB$.

In the given figure, $ABCD$ is a parallelogram, $DC$ is produced to $E$ such that $\angle BCE=105°$. Calculate $\angle A$, $\angle B$, $\angle C$ and $\angle D$.

If one angle of a parallelogram is a right angle, prove that all other angles are right angles​.

$ABCD$ is a rhombus in the given figure. $RABS$ is a straight line such that $RA=AB=BS$, Prove that $RD and SC$ when produced meet at right angle.

Prove that the bisector of the interior angle of a rectangle form a square.

$M and N$ points are taken on the diagonal $AC$ of a parallelogram $ABCD$ such that $AM=CN$. Prove that $BMDN$ is a parallelogram.