Check the picture below.
[tex]\bf \textit{circumference of a circle}\\\\ C=2\pi r~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ r=2.9 \end{cases}\implies C=2\pi (2.9)\implies C=5.8\pi \implies C\approx 18.22 \\\\[-0.35em] ~\dotfill\\\\ ~\hfill \stackrel{C\div r}{18.22\div 2.9 \approx 6.28}\qquad \stackrel{C\div d}{18.22\div 5.8 \approx 3.14}~\hfill[/tex]
