Perimeter of the circle

Calculate the perimeter of the circle in dm, whose radius equals the side of the square containing 0.49 dm²?

Correct answer:

o =  4.3982 dm

Step-by-step explanation:

$$\begin{gathered} S=0.49{\text{dm}}^2 \\ a=\sqrt{S}=\sqrt{0.49}={\displaystyle \frac{7}{10}}=0.7\text{ dm } \\ r=a=0.7={\displaystyle \frac{7}{10}}=0.7\text{ dm } \\ o=2\pi \cdot r=2\cdot 3.1416\cdot 0.7=4.3982\text{ dm} \end{gathered}$$

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