Pole koła obliczamy korzystając z wzoru:

$P=\pi r^2$  

gdzie 

r- długość promienia tego koła

zatem:

a) 

$P=25\pi {\text{km}}^2$  

$25\pi =\pi r^2\mid :\pi$    

$r^2=25\mid \sqrt{}$  

$r=5\text{[km]}$  


b) 

$P=3,24\pi {\text{m}}^2$  

$3,24\pi =\pi r^2\mid :\pi$  

$r^2=3,24\mid \sqrt{}$  

$r=1,8\text{[m]}$  


c) 

$P=\frac{9\pi }{49}{\text{cm}}^2$  

$\frac{9\pi }{49}=\pi r^2\mid :\pi$  

$r^2=\frac{9}{49}\mid \sqrt{}$  

$r=\frac{3}{7}\text{[km]}$  

d) 

$P=1600\pi {\text{cm}}^2$  

$1600\pi =\pi r^2\mid :\pi$  

$r^2=1600\mid \sqrt{}$  

$r=40\text{[cm]}$  


e) 

$P=0,01\pi {\text{km}}^2$  

$0,01\pi =\pi r^2\mid :\pi$  

$r^2=0,01\mid \sqrt{}$  

$r=0,1\text{[km]}$