a)
б)
2. R - радиус, D - диаметр
![image](https://tex.z-dn.net/?f=S%3D+%5Cpi+R%5E2+%3D%3E+R%3D+%5Csqrt%7B+%5Cfrac%7BS%7D%7B+%5Cpi+%7D+%7D+%3D+%5Csqrt%7B+%5Cfrac%7B78%2C5%7D%7B3%2C14%7D+%7D%3D++%5Csqrt%7B25%7D+%3D5+%5C%5C++%5C%5C+D%3D2R%3D2%2A5%3D10)
R= \sqrt{ \frac{S}{ \pi } } = \sqrt{ \frac{78,5}{3,14} }= \sqrt{25} =5 \\ \\ D=2R=2*5=10" alt="S= \pi R^2 => R= \sqrt{ \frac{S}{ \pi } } = \sqrt{ \frac{78,5}{3,14} }= \sqrt{25} =5 \\ \\ D=2R=2*5=10" align="absmiddle" class="latex-formula">
Ответ: радиус=5см, диаметр=10см