Though a line integral on a path P is most easily evaluated when the integrand
can be expressed as a gradient and the integral becomes a difference between values
of a function at the endpoints of P, we here consider the process for reducing
line integrals to ordinary ones. We also describe how to make a Surface flux integral
into a two dimensional integral over an area in the plane.
23.1 Making a Line Integral into an Ordinary
23.3 Practical Comments
23.4 Multiple Integrals and Area Integrals