Rectangle and circle

The rectangle ABCD has side lengths a = 40 mm and b = 30 mm and is circumscribed by a circle k. Calculate approximately how many centimeters a circle is long.

Correct answer:

x =  15.71 cm

Step-by-step explanation:

$$\begin{gathered} a=40\text{mm} \\ b=30\text{mm} \\ d=\sqrt{a^2+b^2}=\sqrt{40^2+30^2}=50\text{mm} \\ o=\pi \cdot d=3.1416\cdot 50\doteq 157.0796\text{mm} \\ x=o\to \text{cm}=o:10\text{cm}=157.0796:10\text{cm}=15.71\text{cm}=15.71\text{cm} \end{gathered}$$

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