A lamp

A lamp shade like that of a frustum has a height of 12 cm and an upper and lower diameter of 10 cm and 20 cm. What area of materials is required to cover the curved surface of the frustum?

Correct answer:

S =  612.6 cm²

Step-by-step explanation:

$$\begin{gathered} h=12\text{cm} \\ {d}_1=10\text{cm} \\ {d}_2=20\text{cm} \\ {r}_1=d_1/2=10/2=5\text{cm} \\ {r}_2=d_2/2=20/2=10\text{cm} \\ s=\sqrt{h^2+(r_2-r_1{)}^2}=\sqrt{12^2+(10-5{)}^2}=13\text{cm} \\ S=\pi \cdot (r_1+r_2)\cdot s=3.1416\cdot (5+10)\cdot 13=612.6{\text{cm}}^2 \end{gathered}$$

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