Cone-shaped 23331

For his birthday, Jirka made a cone-shaped hat out of paper. The side of this cone is 35cm long, and the radius of its base is 20cm. How much dm of paper did Jirka use to make it? Thank you

Correct answer:

x =  21.9911 dm²

Step-by-step explanation:

$$\begin{gathered} s=35\text{cm}\to \text{dm}=35:10\text{dm}=3.5\text{dm} \\ r=20\text{cm}\to \text{dm}=20:10\text{dm}=2\text{dm} \\ x=\pi \cdot r\cdot s=3.1416\cdot 2\cdot 3.5=21.9911{\text{dm}}^2 \end{gathered}$$

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