Module 16 :  Line Integrals, Conservative fields Green's Theorem and applications
Lecture 47 :  Conservative Vector Fields [Section 47.2]
47.2.5 Theorem :
  Let be an open connected subset of and be a continuous vector-field. Then the following statements are equivalent :
(i)
There exists a scalar-field such that

i.e., is conservative.

(ii)
For any two points , the line integral is independent of the path joining and .
(iii)
, for every closed smooth curve in .
  Proof
 

If , then by theorem for any curve joining ,

Hence holds.

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