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Unformatted text preview: of parametric representations with the same orientation.
Note that any curve # gives rise to two oriented curves. Indeed, it is enough
to ﬁx a parametric representation ! : I * RN and considering the equivalence
class # + of parametric representations with the same orientation of ! and the
equivalence class # # of parametric representations with the opposite orientation
Let E ) RN and let g : E * RN be a continuous function. Given a piecewise
C 1 oriented curve # with parametric representation ! : [a, b] * RN such that
! ([a, b]) ) E , we deﬁne
A g := ! A N
b+ gi (! (t)) -! (t) dt.
i a i=1 Deﬁnition 98 Let U ) RN be an open set and let g : U * RN . We say that
g is conservative vector ﬁeld if there exists a di!erentiable function f : U * R
,f (x) = g (x)
for all x ! U . The function f is called a scalar potential for g. Theorem 99 (Fundamental Theorem of Calculus for Curves) Let U )
RN be an open set, let f ! C 1 (U ), let x, y ! U and let # a piecewise C 1 oriented
curve with parametric representation ! : [a, b] * RN such that ! (b) = x,
! (a) = y, and ! ([a, b]) ) U . Then
,f = f (x) ' f (y) .
! Proof. Deﬁne p (t) := f (! (t)) and observe that by Theorem 50, p is piecewise
C 1 with
p! (t) =
(! (t)) -! (t)
i=1 for all but ﬁnitely many t. Hence,
(! (t)) -! (t) dt =
p! (t) dt = p (b)'p (a) = f (x)'f (y) ,
a i=1 # xi
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This document was uploaded on 03/31/2014.
- Spring '14