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As shown in the figure, after a cylinder is cut off 5cm, the surface area of the cylinder is reduced by 31.4cm2
Bottom circumference: 31.4 △ 5 = 6.28 (CM), bottom radius: 6.28 △ 3.14 △ 2 = 1 (CM), two bottom areas: 3.14 × 12 × 2 = 6.28 (cm 2), side area: 6.28 × 20 = 125.6 (cm 2), surface area: 125.6 + 6.28 = 131.88 (cm 2). Answer: the surface area of the original cylinder is 131.88 cm 2
For a cylinder, the bottom diameter is 4cm and the height is 15cm, the surface area and volume are calculated`
The bottom radius of the cylinder is r = 4 / 2 = 2 cm, and the height is h = 15 cm. Therefore, the volume of the cylinder is R ^ 2 * H = 3.14 * 2 * 2 * 15
=4 cm3;
Surface area = 2 μ R ^ 2 + 2 μ RH = 2 μ R (R + H) = 2 * 3.14 * 2 * (2 + 15) = 12.56 * 17 = 213.52 square centimeter
If the diameter of the bottom is 16cm, the height of the cylinder is 18cm
8×8×3.14*2+16*3.14*18
A 15 cm high cylinder is cut into two and a half cylinders along the bottom diameter, and the surface area is increased by 75 cm square. What is the original surface area of the cylinder?
What's the volume?
Diameter of cylinder = 75 △ 2 × 15 = 2.5cm
Radius = 1.25 cm
Original cylinder surface area = 2 * 3.14 * 1.25 * 1.25 + 3.14 * 2.5 * 15 = 127.5625 square centimeter
Original cylinder volume = 3.14 * 1.25 * 1.25 * 15 = 73.59375 cubic cm
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