Circumference Math Example 1

Solution

1. 1
   The circumference is the perimeter of a circle — the distance around it. Two equivalent formulas: $C = 2\pi r$ (using radius) or $C = \pi d$ (using diameter). They are equivalent since $d = 2r$.
2. 2
   Substitute $r = 5$ cm into $C = 2\pi r$: $C = 2\pi(5) = 10\pi$.
3. 3
   Result: $C = 10\pi$ cm $\approx 31.4$ cm. The formula $C = 2\pi r$ encodes the definition of $\pi$ itself: $\pi = C/d$, the ratio of circumference to diameter, which is the same for every circle.