As shown in the figure, after a cylinder is cut off 5cm, the surface area of the cylinder is reduced by 31.4cm square Help me ...

As shown in the figure, after a cylinder is cut off 5cm, the surface area of the cylinder is reduced by 31.4cm square Help me ...

Analysis: after cutting off 5cm, the surface area of the cylinder is reduced by 31.4 square centimeter. In fact, the side area of a cylinder with 5cm height and the same bottom as the original cylinder is reduced. From this, we can calculate the perimeter of the bottom surface, that is, the perimeter L = 31.4 / 5 (CM), the radius of the bottom surface = perimeter / (2 * 3.14) = (31.4 / 5) / (2 * 3.14) = 1 (CM)