In the figure,$ABCD$ and $AEFG$ are two parallelograms. If $\angle C = 55^{\circ},$ determine $\angle F.$ (in $^{\circ}$)

Diagonals of a parallelogram $ABCD$ intersect at $O.$ If $\angle BOC = 90^{\circ}$ and $\angle BDC = 50^{\circ},$ then $\angle OAB$ is (in $^{\circ}$)

In parallelogram $PQRS$,diagonal $PR$ bisects $\angle P$. Prove that diagonal $PR$ bisects $\angle R$ also and $PQRS$ is a rhombus.

Diagonals of a quadrilateral $ABCD$ bisect each other. If $\angle A = 35^{\circ}$,determine $\angle B$. (in $^{\circ}$)

In a rhombus $ABCD$,$\angle B = 80^{\circ}$,then $\angle ADB = \ldots$ (in $^{\circ}$)

Diagonals $AC$ and $BD$ of a parallelogram $ABCD$ intersect each other at $O$. If $OA = 3\, cm$ and $OD = 2\, cm$,determine the lengths of $AC$ and $BD$.