Two circles of radii 12 cm and 13 cm are concentric. The length of the chord of the larger circle which touches the smaller circle is:

In a circle, two chords, AB and CD, measuring 14 cm and 6 cm, respectively, are parallel to each other on the same side of the centre. If the distance between them is 4 cm, find the length (in cm) of the diameter of the circle.​

POR is the diameter of a circle. PQ and RQ are its two chords. The length of arc $$\overline{PQ}$$ is half of the length of are $$\overline{RQ}$$. Find the measure of ∠POQ.​

Two chords of a circle intersect each other at right angles. Chords-segment of first chord are 6 and 5, and chords-segment of second chord are 10 and 3. Then, diameter of circle is