If two bottom surfaces are not included, only the side area of the cylinder is found; If you include two or one circular bottom, you only need the side area+two or one circular area!

Let's find the transverse area without the bottom circle:

The pattern developed on the side of the cylinder is rectangular, and the circumference of the bottom of the cylinder is the width of the rectangle; The height of a cylinder is the length of a rectangle.

Bottom perimeter = rectangular width = π d = π× 20 = 62.8 (cm)

Transverse area = rectangular area = length × width

=40×62.8

= 25 12 (square centimeter)

I hope I can help you!