If two circles are such that the centre of one lies on the circumference of the other, then the ratio of the common chord of two circles to the radius of any of the circles is :

$\mathrm{ABC}$ is a right angled triangle $\mathrm{AB}=3 \mathrm{cm},\mathrm{BC}=5 \mathrm{cm}$ and $\mathrm{AC}=4 \mathrm{cm}$, then the radius of the circle is :

A circle has two parallel chords of lengths $6$ cm and $8$ cm. If the chords are $1$ cm apart and the centre is on the same side of the chords, then the diameter of the circle is of length _____.

Three equal circles of unit radius touch one another.Then the area of the circle circumscribing the three circles is: