A rectangle is 4cm long and 2cm wide. Take its long side as the axis, turn the rectangle for a circle, and get a cylinder with a volume of () A. 8πcm3B. 4πcm3C. 16πcm3D. 12πcm3

A rectangle is 4cm long and 2cm wide. Take its long side as the axis, turn the rectangle for a circle, and get a cylinder with a volume of () A. 8πcm3B. 4πcm3C. 16πcm3D. 12πcm3

According to the volume formula of cylinder, volume = π R2 × height = 4 π × 4 = 16 π cm3

For a cylinder, the sum of its two base areas is equal to the side area. It is known that its surface area is 56 square decimeters

∵ the sum of the two bottom areas is equal to the side area,
Surface area = 4, bottom area = 56,
х base area = 14 = π R & sup2;,
It can be obtained that r = under the root sign (14 / π),
Side area = 28 = 2 π RH,
We can get H = under the root sign (14 / π),
So volume v = bottom area * height = 14 * H = 14 √ (14 / π) cubic decimeter

For a cylinder, the sum of its two bottom areas is equal to the side area. It is known that its surface area is 56 square decimeters?

The surface area is equal to the sum of the two bottom areas plus the side area = 56
So the side area = 2 times the bottom area = 28
The bottom area is 14 = π R & sup2;, so r = 2.11 decimeters
Side area = 2 π R × H = 28
So h = 2.11
Volume = bottom area × height = 14 × 2.11 = 29.54 cubic decimeter