As shown in the diagram,the radii of two concentric circles are $21 \, cm$ and $28 \, cm$. If $m \angle AOB = 40^\circ$,find the area of the shaded region. (in $cm^2$)

Is the area of the circle inscribed in a square of side $a \, cm$ equal to $\pi a^2 \, cm^2$? Give reasons for your answer.

If the area of a circle is $154 \, cm^2$,then its perimeter (circumference) is (in $cm$):

In the figure,$AB$ is a diameter of the circle,$AC = 6 \, cm$ and $BC = 8 \, cm$. Find the area of the shaded region (Use $\pi = 3.14$). (in $cm^2$)

The radius of a circular ground is $56\,m$. $A$ $7\,m$ wide road runs around its boundary inside the ground. Some region of the road as shown by the shaded part in the diagram is to be repaired. Find the cost of repairing at the rate of ₹ $40/m^2$ (in ₹).

As shown in the adjoining diagram,the length of the side of the square plot $ABCD$ is $50 \, m$. At each vertex of the plot,a flower bed in the shape of a sector with radius $10 \, m$ is prepared. Find the area of the plot excluding the flower beds. $(\pi = 3.14)$ (in $m^2$)