Circles and rings in code

You will write short functions for the circumference, the area and the ring. Then you will test the rule for the chord that touches the inner circle.

The idea. The circumference is $2\pi r$. The area is $\pi r^2$. A ring has the area $\pi(R^2 - r^2)$. If a chord of the big circle touches the small circle, the area of the ring is also $\pi$ times the square of half of the chord.

Your tasks.

1. In circumference, return $2\pi r$ rounded to $4$ decimals.
2. In area, return $\pi r^2$ rounded to $4$ decimals.
3. In ring_area, return the area of the ring with outer radius big and inner radius small, rounded to $4$ decimals.
4. Set widest to the name of the ring in rings that has the largest area.