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Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

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Sec. 9]____L<strong>in</strong>e Inlegtah____275<br />

where C is the upper half of the ellipse *--=a cost, y = b s<strong>in</strong>* traversed<br />

clockwise.<br />

Solution. We have<br />

y 2 dx + x* 2 2<br />

dy = [b s<strong>in</strong> t-(a s<strong>in</strong> /) + a 2 cos 2 / -b cos /] dt =<br />

n oo<br />

= ab* f s<strong>in</strong> 8 1 dt + a*b C cos 8 / dt = -t a&.<br />

jt ?t<br />

3. The case of a total differential. If the <strong>in</strong>tegrand of a l<strong>in</strong>e <strong>in</strong>tegral<br />

of the second type is a total differential of some s<strong>in</strong>gle-valued function<br />

U^--U(x, */), that is, P (x, y)dx-\-Q(x, y)dy-=dU(x, y], then this l<strong>in</strong>e <strong>in</strong>tegral<br />

is not dependent on the path of <strong>in</strong>tegration and we have the Newton-Leibniz<br />

formula<br />

(x2 , yj<br />

P(x, y)dx + Q(x, y)dy = U(x 2 , yJ U (x l9

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