Circle - simple

Calculate the area of a circle in dm² if its circumference is 31.4 cm.

Correct answer:

S =  0.78 dm²

Step-by-step explanation:

$$\begin{gathered} 31.4=2\pi r \\ r=0.5dm \\ S=\pi r^2=0.78{\text{dm}}^2 \end{gathered}$$

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