The total surface are of cylinder comprises of the lateral or curved surface area + the area of the flat surface on the top and bottom
The lateral surface area is calculated this way
curved area of the face × height
Here it is a circle and hence its circumference is 2πr
Hence the formula become
2πr × h = 2πrh
So 2πrh is the part that represents the curved area of the cylinder
(Additional info: The area of the faces is given by πr² for one side, since a cylinder has 2 faces
we have πr²+πr²=2πr²
Hence the total surface area is 2πrh +2πr²)
