Question

Find the area if the following circle circumference = 280cm find r from c

Answer 1

`\textit{circumference of a circle}\\\\ C=2\pi r ~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ C=280 \end{cases}\implies 280=2\pi r\implies \cfrac{280}{2\pi }=r\implies \cfrac{140}{\pi }=r \\\\[-0.35em] ~\dotfill\\\\ \textit{area of a circle}\\\\ A=\pi r^2 ~~ \begin{cases} r=radius\\[-0.5em] \hrulefill\\ r=(140)/(\pi ) \end{cases}\implies A=\pi \left( \cfrac{140}{\pi } \right)^2 \\\\\\ A=\pi \cdot \cfrac{140^2}{\pi^2}\implies A=\cfrac{19600}{\pi }\implies A\approx 6238.87~cm^2`