Module 17 : Surfaces, Surface Area, Surface integrals, Divergence Theorem and applications
Lecture 50 :  Surface Integrals [Section 50.1]
 

and

                                              ----------(65)

this gives,

                                             ----------(66)

Using we have

                                 ----------(67)

where is the acute angle between , the normal to , and . From and , we have



Hence, gives us the relation

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