Circles, circumference

Question

A cardboard tube is used to mail a poster. The diameter of the tube is 7 cm and its length is 1.2 m. What is the Surface area of the tube?

Answer 1

For any solid where the cross-section does not vary with the length, the surface area has 2 components:

--the area of the ends

--the are from one end to the other, which is the perimeter of one end times the length

So--for a cylinder with both ends closed: r = radius of the end, l = length

Area of end: 2 * pi * r^2

Area end-to-end: 2 * pi * r * l

TOTAL Area: 2 * pi * r (r + l)