First, I divide 12.56 by 4 to calculate the perimeter of the bottom surface is 3. 14dm, then divide 3. 14 by 6.28 to calculate the radius of the bottom surface is 0.5dm, and then use 3. 14x0.5x0.5=0.785dm? Finally, use12.56+0.785 =13.345dm?

2. Split a log with a length of 1m into two equal halves along the diameter, and increase the surface area by 0.8m? . What is the original surface area of this log?

First, I divide 0.8 by 2 to calculate that the area of a dividing surface is 0.4m? Divide 0.4 by 1 to calculate the bottom radius =0.4m, divide 0.4 by 2 to calculate the bottom radius =0.2m, and then calculate that the two bottom areas are 0. 1256m? , calculate the transverse area 1.256m? Finally, add the two bottom areas and lateral area together to get 1.438+06m?

3. The radius of the bottom surface of the cylindrical water cup is 4cm and the height is 10cm. If the water level in the cup is 5cm, what is the contact area between the inner wall and water?

I use 3. 14X4? Calculate the bottom area, because as long as you pour it in, you will encounter the top and bottom =50.24cm? , and then use 5x3. 14x8 to calculate the area of water contacting the side of the cup = 125.6cm? , and finally add up to 175.84cm?