Cut a 1-meter-long cylindrical steel with a bottom diameter of 2 decimeters into two sections and increase its surface area () A. 6.28 square decimeters B. 9.42 square decimeters C. 12.56 square decimeters

Cut a 1-meter-long cylindrical steel with a bottom diameter of 2 decimeters into two sections and increase its surface area () A. 6.28 square decimeters B. 9.42 square decimeters C. 12.56 square decimeters

3.14 × (2 △ 2) 2 × 2 = 3.14 × 1 × 2 = 6.28 (square decimeter) a: the surface area increases by 6.28 square decimeter