We know that the circumfrence of a circle equals pi times two.
So how can we rearrange this?
I will substitute pi with 3.14 to make it easier.
is the original equation.
To make the radius come first, we can the circumfrence by
.
would be the answer.
We can check that:
Suppose r=6
![C = 2(3.14)6\\6.28 (6)\\=37.68](https://img.qammunity.org/2021/formulas/mathematics/middle-school/ov08h2yeq8aklrlwg9hcp5mhq0m58fley4.png)
If the circumfrence is 37.68, we can plug it in to the formula we found.
![6 = (37.68)/(2(3.14)) \\6 = (37.68)/(6.28) \\6 = 6](https://img.qammunity.org/2021/formulas/mathematics/middle-school/n43wyvxnjc3ojyk3yd2lx0feumgbkqxwn1.png)
It's correct! The answer is the third one!