Răspuns:
Explicație pas cu pas:
[tex]\displaystyle A=\pi\times r^{2} =\pi \times (\frac{d}{2} )^2=\frac{\pi\times d^{2} }{4}[/tex]
d-diametru si r-raza
a)d=8 cm
[tex]\displaystyle A=\frac{\pi \times 8^{2} }{4} =16\pi cm^{2}[/tex]
b)d=1,4cm
[tex]\displaystyle A=\frac{\pi \times 1,4^{2} }{4} =0,49\pi cm^{2}[/tex]
c)d=4,(4) cm
[tex]\displaystyle 4,(4)^{2} =(\frac{40}{9} )^2=\frac{1600}{81} \\\displaystyle A=\frac{\pi \times 4,(4)^{2} }{4} =\frac{\pi\times \frac{1600}{81} }{4} =\frac{\pi\times 1600 }{81\times 4} =\frac{400}{81} \times \pi cm^{2}[/tex]
