In the given figure, two concentric circles with centre O have radii 14 cms and 7 cms. If $\angle AOB = 30^{\circ}$, find the area of the shaded region. <img src="https://balti.afterboards.in/1T5AYxgGaTmwIut" width="400px"/>

The pair of tangents drawn from an external point to a circle are perpendicular to each other and the length of each tangent (from the point to the circle) is 5 cm. The radius of the circle is

If the radii of two concentric circles are 4 cm and 5 cm, then the length of a chord of one circle that is tangent to the other circle is

From the given figure, find the length of the major arc AB

If the perimeter of a circle changed from $4\pi$ to $8\pi$, then what is the change in its area?