Surface Area of a Right Circular Cylinder

If we take a number of circular sheets of paper and stack them up as we stacked up rectangular sheets earlier, what would we get (see Fig.)

Here, if the stack is kept vertically up, we get what is called a right circular cylinder, since it has been kept at right angles to the base, and the base is circular. Let us see what kind of cylinder is not a right circular cylinder.
In Fig (a), you see a cylinder, which 
is certainly circular, but it is not at right angles to the base. So, we can not say this a right circular cylinder.

Of course, if we have a cylinder with a non circular base, as you see in Fig (b). then we also cannot call it a right circular cylinder.
So curved surface area of the cylinder = area of the rectangular sheet = length × breadth
 = perimeter of the base of the cylinder x h    

Where r is the radius of the base of the cylinder and h is the height of the cylinder.

Where h is the height of the cylinder and r its radius.