A rectangular paper is folded into a cylinder. The length and breadth of the paper are L and B respectively. What is the outer surface area of the cylinder?
LB
The cylinder is a 3-D object. To find its surface area, we need to convert it into a 2-D plane. Here the 3-D surface of cylinder can be unrolled into a 2-D rectangular sheet of paper. The area of the 3-D surface and that of the 2-D plane are the same.
It is clear that area of rectangle
= Length × Breadth
= LB