Chords and the centre

You will write functions that link the radius of a circle, the length of a chord and its distance from the centre. Then you will find the angle a chord makes at the centre.

The idea. The perpendicular from the centre bisects the chord, so $r^2 = d^2 + \left(\dfrac{c}{2}\right)^2$. The angle at the centre follows from the right triangle: half of it has the sine $\dfrac{c/2}{r}$.

Your tasks.

1. In chord_length, return the length of the chord at distance distance from the centre, rounded to $6$ decimals.
2. In distance_to_chord, return the distance from the centre of a chord of length chord, rounded to $6$ decimals.
3. In centre_angle, return the angle in degrees that the chord makes at the centre, rounded to $4$ decimals.
4. Set longest to the name of the chord in distances that is the longest.