Alternative to remember area and circumference of a circle

Many people can actually remember either:

`pir^2` or `2pir`

But need a nudge to remind them which is area and which is circumference.

To remember which is which:

Just remember `r^2` must be an area

And a single `r` must be a line

So

`\pir^2` = Area

`2\pir` = The line of the circumference