Question

What are two formulas for finding the circumfrence of a circle?

Answer 1

`C=2pir, C=pid`

Explanation:

The standard formula is

`C=2pir` where `r` is the radius.

There is, however, a second formula that produces the same result.

Recall that the diameter is two times the radius, or `d=2r`

Well, in the formula `C=2pir=2rpi,` `2r` does show up, and since `d=2r,` we can simply replace it with `d.`

`C=pid`