1, cylinder volume: v = s * h = pi * r 2 * h (pi is 3. 14 159, so pi is used instead because it cannot be typed).

S is the area of a circle and h is the height of a cylinder.

You can imagine that a cylinder is made up of n circles, and the height of each circle is h/n, then the height of their superposition is H.

2. The surface area of a cylinder is the area of two circles plus a rectangle.

The length of a rectangle is the circumference of a circle and the width is the height of a cylinder.

When you start to remove two circles from the cylinder, it is a rectangle, its length is the circumference of the circle, and its width is the height of the cylinder.