The lateral surface area of a right circular cylinder is given by which expression?

• A. 2π r h
• B. 2π r (r + h)
• C. π r^2
• D. π r h

Answer: (A)

The key idea is that lateral surface area comes from the side surface, which you can think of by unwrapping the cylinder’s side into a rectangle. The height of that rectangle is the cylinder’s height h, and its width is the circumference of the circular cross-section, which is 2πr. So the area is width times height: (2πr)·h = 2πrh. That gives the lateral surface area.

The other expressions correspond to other parts or quantities: πr^2 is the area of one base, and 2πr(r+h) is the total surface area (lateral plus both bases). πrh isn’t the correct measurement for the side surface because it misses the full circumference factor.