Expand the side of a cylinder to get a square. It is known that the bottom area of the cylinder is 20 square centimeters. What is the surface area of the cylinder?

Expand the side of a cylinder to get a square. It is known that the bottom area of the cylinder is 20 square centimeters. What is the surface area of the cylinder?

Finding the radius of a cylinder
πr²＝20 r²＝20/π
Find the perimeter of the bottom edge
L＝2πr L＝2×π×r
Side area of cylinder
L×L＝（2πr）²
＝4π²×20/π
＝80π
Surface area of cylinder
80π＋20×2
＝80π＋40
A: the surface area of this cylinder is (80 π + 40) square centimeters

If the height of a cylinder is reduced by one centimeter, the surface area will be reduced by 125.6 square centimeters. What is the surface area of the cylinder

In fact, the decrease of height means the decrease of side area and the constant of bottom area, so the perimeter of bottom surface is 125.6 △ 4 = 31.4cm. The radius is 31.4 △ 3.14 △ 2 = 5cm, so the bottom area is 3.14 × 5 & # 178; = 78.5cm

As shown in the figure, after a cylinder is cut off 6cm, its surface area is reduced by 75.36cm2. What is the original surface area of the cylinder? Its height is 22cm

Cut off 6cm is high, then cut off the bottom is not cut off, is still two bottom. Then 75.36 square cm = side area
Known side area and height of base perimeter: 75.36 △ 6 = 12.56 cm, known perimeter of two base areas: 12.56 △ 3.14 △ 2 = 2 cm (radius) 2 × 2 × 3.14 × 2 = 25.12 square cm (two base areas)
The height is 22 cm, and the side area = the perimeter of the bottom surface × the height is 12.56 × 22 = 276.32 square cm
Surface area: 276.32 + 25.12 = 301.44 square centimeter
I hope my answer can help you. Helping you is my happiness,