Two concentric circles are of diameters $30 \mathrm{cm}$ and $18 \mathrm{cm}$. Find the length of the chord of the larger circle which touches the smaller circle.

In the figure, a $∆ABC$ is drawn to circumscribe a circle of radius 4cm such that the segments $BD$ and $DC$ are of lengths $8 \mathrm{cm}$ and $6 \mathrm{cm}$ respectively. Find the lengths of sides $AB$ and $AC$, when area of $∆ABC$ is $84 {\mathrm{cm}}^2$.

Is it possible, that the angle between two tangents drawn to a circle may be $0°$?

In how many points, does a line intersect the circle at most?

A line, which intersects the circle in two points, is called as _____.