Question

Question #726e8

Answer 1

They have a ratio that only depends on the radius (diameter).

Any circle with a given radius `R` (=half the diameter `D`)
will have a circumference of `P=2piR = piD`
and a surface area of `A=piR^2=1/4piD^2`

The ratio between the two:

Surface/Circumference=`A/P=(piR^2)/(2piR)=R/2=1/2 R`

Circumference/Surface=`P/A=(2piR)/(piR^2)=2/R`

Since radius `R` translates to half the diameter `D`:

`A/P=1/4D` and `P/A=4/D`