As shown in the diagram,$\overline{ OA }$ and $\overline{ OB }$ are two radii of $\odot( O , 21 \text{ cm} )$ perpendicular to each other. If $OD = 10 \text{ cm}$,find the area of the shaded region. (in $\text{cm}^2$)

In $\odot(O, r)$,chord $\overline{AB}$ subtends a right angle at the centre. The area of the minor segment $\overline{AB} \cup \widehat{ACB}$ is $114 \, cm^2$ and the area of $\Delta OAB$ is $200 \, cm^2$. Then,the area of the minor sector $OACB$ is ......... $cm^2$.

In the figure,arcs have been drawn with radii $14 \, cm$ each and with centres $P$,$Q$,and $R$. Find the area of the shaded region (in $cm^{2}$).

Area of a sector of central angle $200^{\circ}$ of a circle is $770 \, cm^{2}$. Find the length of the corresponding arc of this sector. (in $cm$)

Find the area of a sector of a circle of radius $21 \, cm$ and central angle $120^{\circ}$. (in $cm^{2}$)

The circumference of a circle is $251.2 \, cm$. Find its diameter. $(\pi = 3.14)$ (in $cm$)