$ABCD$ is a parallelogram as shown in the figure. Find the values of $x$ and $y$.

$RICE$ is a rhombus. Find $x,y$ and $z$, justify your answers. Also, find the perimeter of the rhombus.

In the adjacent figure, both $RISK$ and $CLUE$ are parallelograms. Find the value of $x$.

In the given figure, the value of $x$ is

In the given figure, if $\mathrm{ABC}$ and $\mathrm{DEF}$ are two straight lines, then the value of $x$ is 

In the given figure, if $ABCD$ is a rhombus, then the value of $(x-y)$ is 

In a square $\mathrm{ABCD}$, if the diagonals bisect at $\mathrm{O}$. Then $∆\mathrm{AOB}$ is

For which of the following quadrilaterals, diagonals are perpendicular to each other?

A quadrilateral whose all sides are equal, opposite angles are equal and the diagonals bisect each other at right angles is a _____.