Question

How do you find the circumference and the area of a circle with diameter 6m?

Answer 1

Area of circle = `pir^2` or `pi (d/2)^2`
Circumference of circle = `pid`
For a circle with diameter `6`m this becomes `A~=28.27m^2` and `C~=18.85m`

Explanation:

The constant `pi ~=3.14159` is the ratio of the circumference of a circle to its diameter (or equivalently to twice it's radius).

`C=pid = pi2r`

That same value, `pi`, is also the ratio of the the area of a circle to the square of its radius

`A=pir^2`

Plugging the given diameter (or diameter divided by 2 for the radius) into these equations gives the required results.