Surface Area integral of revolution

68 Views Asked by At

I have a problem understanding the definition of the surface area integral of a revolution . I know that we can obtain its volume using the disc method . The method defines the width of the disc as infinitely small (dx) , it is then pretty obvious that the integral is defined as the area made by each point multiplied by the width , which is dx .I found however by the definition of the surface area integral that the width is not defined as dx . Can somebody please clarify why it doesn't work the same way with surface areas ? ! thanks