The circumference of a circle is $176 \, cm$. Find its radius in $cm$.

If $\theta$ is the angle (in degrees) of a sector of a circle of radius $r$,then the area of the sector is:

The radii of two concentric circles are $14 \, cm$ and $10.5 \, cm$. Then,the difference between their circumferences is $\ldots \ldots \ldots \, cm$.

$\widehat{ACB}$ is a minor arc of $\odot(O, 8 \, cm)$. If $m\angle AOB = 45^\circ$, the length of minor $\widehat{ACB}$ is $\dots \, cm$. (in $\pi$)

The central angles of two sectors of circles of radii $7 \, cm$ and $21 \, cm$ are respectively $120^{\circ}$ and $40^{\circ}$. Find the areas of the two sectors as well as the lengths of the corresponding arcs. What do you observe?

In a circle with radius $11.2 \, cm$,two radii are perpendicular to each other. Find the area of the minor sector,the major sector,and the minor segment corresponding to these radii.